Lithium metal secondary battery containing an electrochemically stable anode-protecting layer

ABSTRACT

Provided is a lithium secondary battery, comprising a cathode, an anode, and a porous separator or electrolyte, wherein the anode comprises: (a) an anode active layer containing a layer of lithium or lithium alloy, in a form of a foil, coating, or multiple particles aggregated together, as an anode active material; and (b) an anode-protecting layer of a conductive sulfonated elastomer composite, disposed between the anode active layer and the separator/electrolyte; wherein the composite has from 0.01% to 40% by weight of a conductive reinforcement material and from 0.01% to 40% by weight of an inorganic filler dispersed in a sulfonated elastomeric matrix material and the protecting layer has a thickness from 1 nm to 100 μm, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10 −7  S/cm to 5×10 −2  S/cm, and an electrical conductivity from 10 −7  S/cm to 100 S/cm.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 16/014,614, filed Jun. 21, 2018, which is herebyincorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to the field of rechargeable lithium metalbattery having a lithium metal layer (in a form of thin lithium foil,coating, or sheet of lithium particles) as an anode active material anda method of manufacturing same.

BACKGROUND OF THE INVENTION

Lithium-ion and lithium (Li) metal cells (including lithium metalsecondary cell, lithium-sulfur cell, lithium-selenium cell, Li-air cell,etc.) are considered promising power sources for electric vehicle (EV),hybrid electric vehicle (HEV), and portable electronic devices, such aslap-top computers and mobile phones. Lithium metal has the highestcapacity (3,861 mAh/g) compared to any other metal or metal-intercalatedcompound (except Li_(4.4)Si) as an anode active material. Hence, ingeneral, rechargeable Li metal batteries have a significantly higherenergy density than lithium ion batteries.

Historically, rechargeable lithium metal batteries were produced usingnon-lithiated compounds having high specific capacities, such as TiS₂,MoS₂, MnO₂, CoO₂ and V₂O₅, as the cathode active materials, which werecoupled with a lithium metal anode. When the battery was discharged,lithium ions were dissolved from the lithium metal anode and transferredto the cathode through the electrolyte and, thus, the cathode becamelithiated. Unfortunately, upon cycling, the lithium metal resulted inthe formation of dendrites that ultimately caused unsafe conditions inthe battery. As a result, the production of these types of secondarybatteries was stopped in the early 1990's giving ways to lithium-ionbatteries.

Even now, cycling stability and safety concerns remain the primaryfactors preventing the further commercialization of Li metal batteriesfor EV, HEV, and microelectronic device applications. These issues areprimarily due to the high tendency for Li to form dendrite structuresduring repeated charge-discharge cycles or an overcharge, leading tointernal electrical shorting and thermal runaway. Many attempts havebeen made to address the dendrite-related issues, as briefly summarizedbelow:

Fauteux, et al. [D. Fauteux, et al., “Secondary Electrolytic Cell andElectrolytic Process,” U.S. Pat. No. 5,434,021, Jul. 18, 1995] appliedto a metal anode a protective surface layer (e.g., a mixture ofpolynuclear aromatic and polyethylene oxide) that enables transfer ofmetal ions from the metal anode to the electrolyte and back. The surfacelayer is also electronically conductive so that the ions will beuniformly attracted back onto the metal anode during electrodeposition(i.e. during battery recharge). Alamgir, et al. [M. Alamgir, et al.“Solid polymer electrolyte batteries containing metallocenes,” U.S. Pat.No. 5,536,599, Jul. 16, 1996] used ferrocenes to prevent chemicalovercharge and dendrite formation in a solid polymer electrolyte-basedrechargeable battery.

Skotheim [T. A. Skotheim, “Stabilized Anode for Lithium-PolymerBattery,” U.S. Pat. No. 5,648,187 (Jul. 15, 1997); U.S. Pat. No.5,961,672 (Oct. 5, 1999)] provided a Li metal anode that was stabilizedagainst the dendrite formation by the use of a vacuum-evaporated thinfilm of a Li ion-conducting polymer interposed between the Li metalanode and the electrolyte. Skotheim, et al. [T. A. Skotheim, et al.“Lithium Anodes for Electrochemical Cells,” U.S. Pat. No. 6,733,924 (May11, 2004); U.S. Pat. No. 6,797,428 (Sep. 28, 2004); U.S. Pat. No.6,936,381 (Aug. 30, 2005); and U.S. Pat. No. 7,247,408 (Jul. 24, 2007)]further proposed a multilayer anode structure consisting of a Limetal-based first layer, a second layer of a temporary protective metal(e.g., Cu, Mg, and Al), and a third layer that is composed of at leastone layer (typically 2 or more layers) of a single ion-conducting glass,such as lithium silicate and lithium phosphate, or polymer. It is clearthat such an anode structure, consisting of at least 3 or 4 layers, istoo complex and too costly to make and use.

Protective coatings for Li anodes, such as glassy surface layers ofLiI—Li₃PO₄—P₂S₅, may be obtained from plasma assisted deposition [S. J.Visco, et al., “Protective Coatings for Negative Electrodes,” U.S. Pat.No. 6,025,094 (Feb. 15, 2000)]. Complex, multi-layer protective coatingswere also proposed by Visco, et al. [S. J. Visco, et al., “ProtectedActive Metal Electrode and Battery Cell Structures with Non-aqueousInterlayer Architecture,” U.S. Pat. No. 7,282,295 (Oct. 16, 2007); U.S.Pat. No. 7,282,296 (Oct. 16, 2007); and U.S. Pat. No. 7,282,302 (Oct.16, 2007)].

Despite these earlier efforts, no rechargeable Li metal batteries haveyet succeeded in the market place. This is likely due to the notion thatthese prior art approaches still have major deficiencies. For instance,in several cases, the anode or electrolyte structures are too complex.In others, the materials are too costly or the processes for makingthese materials are too laborious or difficult. Solid electrolytestypically have a low lithium ion conductivity, are difficult to produceand difficult to implement into a battery.

Furthermore, solid electrolyte, as the sole electrolyte in a cell or asan anode-protecting layer (interposed between the lithium film and theliquid electrolyte) does not have and cannot maintain a good contactwith the lithium metal. This effectively reduces the effectiveness ofthe electrolyte to support dissolution of lithium ions (during batterydischarge), transport lithium ions, and allowing the lithium ions tore-deposit back to the lithium anode (during battery recharge).

Another major issue associated with the lithium metal anode is thecontinuing reactions between electrolyte and lithium metal, leading torepeated formation of “dead lithium-containing species” that cannot bere-deposited back to the anode and become isolated from the anode. Thesereactions continue to irreversibly consume electrolyte and lithiummetal, resulting in rapid capacity decay. In order to compensate forthis continuing loss of lithium metal, an excessive amount of lithiummetal (3-5 times higher amount than what would be required) is typicallyimplemented at the anode when the battery is made. This adds not onlycosts but also a significant weight and volume to a battery, reducingthe energy density of the battery cell. This important issue has beenlargely ignored and there has been no plausible solution to this problemin battery industry.

Clearly, an urgent need exists for a simpler, more cost-effective, andeasier-to-implement approach to preventing Li metal dendrite-inducedinternal short circuit and thermal runaway problems in Li metalbatteries, and to reducing or eliminating the detrimental reactionsbetween lithium metal and the electrolyte.

Hence, an object of the present invention was to provide an effectiveway to overcome the lithium metal dendrite and reaction problems in alltypes of Li metal batteries having a lithium metal anode. A specificobject of the present invention was to provide a lithium metal cell thatexhibits a high specific capacity, high specific energy, high degree ofsafety, and a long and stable cycle life.

SUMMARY OF THE INVENTION

Herein reported is a lithium metal secondary battery, comprising acathode, an anode, and an electrolyte or separator-electrolyte assemblydisposed between the cathode and the anode, wherein the anode comprises:(a) a layer of lithium or lithium alloy (in the form of a foil, coating,or multiple particles aggregated together) as an anode active materiallayer; and (b) a separate and discrete anode-protecting layer comprisinga conductive sulfonated elastomer composite having from 0.01% to 40% byweight of a conductive reinforcement material and from 0.01% to 40% byweight of an electrochemically stable inorganic filler dispersed in asulfonated elastomeric matrix material and the layer of conductivesulfonated elastomer composite has a thickness from 1 nm to 100 μm, afully recoverable tensile strain from 2% to 500%, a lithium ionconductivity from 10⁻⁷ S/cm to 5×10⁻² S/cm, and an electricalconductivity from 10⁻⁷ S/cm to 100 S/cm when measured at roomtemperature, wherein the anode-protecting layer is disposed between theanode active material layer (i.e. the lithium or lithium alloy layer)and the electrolyte or separator-electrolyte assembly layer. The foil orcoating of lithium or lithium alloy may be supported by a currentcollector (e.g. a Cu foil, a Ni foam, a porous layer of nanofilaments,such as graphene sheets, carbon nanofibers, carbon nanotubes, etc.). Aporous separator may not be necessary if the electrolyte is asolid-state electrolyte.

For defining the claims, the invented lithium metal secondary batterydoes not include a lithium-sulfur cell or lithium-selenium cell. Assuch, the cathode does not include sulfur, lithium polysulfide, seleniumand lithium polyselenide.

The sulfonated elastomer is a high-elasticity material which exhibits anelastic deformation that is at least 2% (preferably at least 5% and upto approximately 800%) when measured under uniaxial tension. In thefield of materials science and engineering, the “elastic deformation” isdefined as a deformation of a material (when being mechanicallystressed) that is essentially fully recoverable upon release of the loadand the recovery process is essentially instantaneous (no or little timedelay). The elastic deformation is more preferably greater than 10%,even more preferably greater than 30%, further more preferably greaterthan 50%, and still more preferably greater than 100%.

Preferably, the conductive reinforcement material is selected fromgraphene sheets, carbon nanotubes, carbon nanofibers, carbon or graphitefibers, expanded graphite flakes, metal nanowires, conductive polymerfibers, or a combination thereof.

In some embodiments, the sulfonated elastomer composite preferably andmore typically has a fully recoverable tensile strain from 5% to 300%(most typically from 10% to 150%), a thickness from 10 nm to 20 μm, alithium ion conductivity of at least 10⁻⁵ S/cm, and an electricalconductivity of at least 10⁻³ S/cm when measured at room temperature ona cast thin film 20 μm thick.

Preferably, the sulfonated elastomeric matrix material contains asulfonated version of an elastomer selected from natural polyisoprene,synthetic polyisoprene, polybutadiene, chloroprene rubber,polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber,ethylene propylene rubber, ethylene propylene diene rubber,metallocene-based poly(ethylene-co-octene) (POE) elastomer,poly(ethylene-co-butene) (PBE) elastomer,styrene-ethylene-butadiene-styrene (SEBS) elastomer, epichlorohydrinrubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber,perfluoroelastomers, polyether block amides, chlorosulfonatedpolyethylene, ethylene-vinyl acetate, thermoplastic elastomer, proteinresilin, protein elastin, ethylene oxide-epichlorohydrin copolymer,polyurethane, urethane-urea copolymer, or a combination thereof. Thesesulfonated elastomers or rubbers, when present without graphene sheets,exhibit a high elasticity (having a fully recoverable tensile strainfrom 2% to 800%). In other words, they can be stretched up to 800% (8times of the original length when under tension) and, upon release ofthe tensile stress, they can fully recover back to the originaldimension. By adding from 0.01% to 50% by weight of a conductivereinforcement material and/or a lithium ion-conducting species dispersedin a sulfonated elastomeric matrix material, the fully recoverabletensile strains are typically reduced down to 2%-500% (more typicallyfrom 5% to 300% and most typically from 10% to 150%).

The conducting reinforcement material is preferably in a nanofilamentaryor nanosheet-like form, such as a nanotube, nanofiber, nanowire,nanoplatelet, or nanodisc. In some embodiments, the conductivereinforcement material is selected from graphene sheets, carbonnanotubes, carbon nanofibers, carbon or graphite fibers, expandedgraphite flakes, metal nanowires, conductive polymer fibers, or acombination thereof. These are electron-conducting materials and thesulfonated elastomer matrix is a lithium ion- and sodium ion-conductingmaterial. By combining such a sulfonated elastomer and a conductingreinforcement, one obtains a composite that is both electron conductingand ion-conducting and capable of allowing electrons and lithium ions tomigrate in and out of the particulate without much resistance.

The graphene sheets to be dispersed in a sulfonated elastomer matrix arepreferably selected from pristine graphene, graphene oxide, reducedgraphene oxide, graphene fluoride, graphene chloride, nitrogenatedgraphene, hydrogenated graphene, doped graphene, functionalizedgraphene, or a combination thereof. The graphene sheets preferablycomprise single-layer graphene or few-layer graphene, wherein thefew-layer graphene is defined as a graphene platelet formed of less than10 graphene planes. The carbon nanotubes (CNTs) can be a single-walledCNT or multi-walled CNT. The carbon nanofibers may be vapor-grown carbonnanofibers or electrospinning based carbon nanofibers (e.g. electrospunpolymer nanofibers that are subsequently carbonized).

In some embodiments, the conductive reinforcement material is selectedfrom graphene sheets, carbon nanotubes, carbon nanofibers, metalnanowires, conductive polymer fibers, or a combination thereof. Theseare electron-conducting materials and the sulfonated elastomer matrix isa lithium ion-conducting material. By combining such a sulfonatedelastomer and a conducting reinforcement, one obtains a composite thatis both electron conducting and ion-conducting and capable of allowingelectrons and lithium ions to migrate in and out of the anode-protectinglayer without much resistance. Additionally, the electrochemicallystable inorganic filler can impart stability to the anode and thebattery when being charged and discharged.

In certain embodiments, the electrically conducting material may beselected from an electron-conducting polymer, a metal particle or wire(or metal nanowire), a graphene sheet, a carbon fiber, a graphite fiber,a carbon nanofiber, a graphite nanofiber, a carbon nanotube, a graphiteparticle, an expanded graphite flake, an acetylene black particle, or acombination thereof. The electrically conducting material (e.g. metalnanowire, nanofiber, etc.) preferably has a thickness or diameter lessthan 100 nm.

In certain embodiments, the inorganic filler has a lithium intercalationpotential no less than 1.1 V versus Li/Li⁺ (preferably from 1.1 V to 4.5V, more preferably from 1.1 to 3.5 V, and most preferably from 1.1 to2.5 V). The presence of this inorganic filler makes the anode-protectinglayer significantly more electrochemically stable.

The inorganic filler is preferably selected from an oxide, carbide,boride, nitride, sulfide, phosphide, or selenide of a transition metal,a lithiated version thereof, or a combination thereof. Preferably, thetransition metal is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y,Zr, Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, a combination thereof, ora combination thereof with Al, Ga, In, Sn, Pb, Sb, or Bi.

Preferably, particles of this inorganic filler are in a form ofnanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt,nanoribbon, nanodisc, nanoplatelet, or nanohorn having a dimension(diameter, thickness, or width, etc.) less than 100 nm, preferably lessthan 10 nm.

This sulfonated elastomer composite layer may be a thin film disposedagainst a lithium foil/coating layer surface or a thin coating depositedon the lithium foil/coating surface. It may be noted that lithiumfoil/coating layer may decrease in thickness due to dissolution oflithium into the electrolyte to become lithium ions as the lithiumbattery is discharged, creating a gap between the current collector andthe protective layer if the protective layer were not elastic. Such agap would make the re-deposition of lithium ions back to the anodeimpossible. We have observed that the instant sulfonated elastomercomposite is capable of expanding or shrinking congruently orconformably with the anode layer. This capability helps to maintain agood contact between the current collector (or the lithium film itself)and the protective layer, enabling the re-deposition of lithium ionswithout interruption.

The sulfonated elastomer composite may further contain a lithium saltselected from lithium perchlorate (LiClO₄), lithium hexafluorophosphate(LiPF₆), lithium borofluoride (LiBF₄), lithium hexafluoroarsenide(LiAsF₆), lithium trifluoro-metasulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃ SO₂)₂), lithiumbis(oxalato)borate(LiBOB), lithium oxalyldifluoroborate (LiBF₂C₂O₄),lithium oxalyldifluoroborate (LiBF₂C₂O₄), lithium nitrate (LiNO₃),Li-fluoroalkyl-phosphates (LiPF₃(CF₂CF₃)₃), lithiumbisperfluoro-ethysulfonylimide (LiBETI), lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, or a combination thereof.

At the anode side, preferably and typically, the sulfonated elastomercomposite for the protective layer has a lithium ion conductivity noless than 10⁻⁵ S/cm, more preferably no less than 10⁻⁴ S/cm, and mostpreferably no less than 10⁻³ S/cm. Some of the selected sulfonatedelastomer composites exhibit a lithium-ion conductivity greater than10⁻² S/cm. In some embodiments, the sulfonated elastomer composite is anelastomer containing no additive or filler dispersed therein. In others,the sulfonated elastomer composite is an elastomer matrix compositecontaining from 0.1% to 40% by weight (preferably from 1% to 30% byweight) of a lithium ion-conducting additive dispersed in a sulfonatedelastomer matrix material. In some embodiments, the sulfonated elastomercomposite contains from 0.1% by weight to 10% by weight of areinforcement nanofilament selected from carbon nanotube, carbonnanofiber, graphene, or a combination thereof.

In some embodiments, the sulfonated elastomer matrix material isselected from a sulfonated version of natural polyisoprene (e.g.cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprenegutta-percha), synthetic polyisoprene (IR for isoprene rubber),polybutadiene (BR for butadiene rubber), chloroprene rubber (CR),polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber (copolymerof isobutylene and isoprene, IIR), including halogenated butyl rubbers(chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, proteinelastin, ethylene oxide-epichlorohydrin copolymer, polyurethane,urethane-urea copolymer, and combinations thereof.

In some embodiments, the sulfonated elastomer composite further containsa lithium ion-conducting additive dispersed in a sulfonated elastomercomposite matrix material, wherein the lithium ion-conducting additiveis selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1 and 1≤y≤4.

The sulfonated elastomer composite may form a mixture, blend,co-polymer, or semi-interpenetrating network (semi-IPN) with anelectron-conducting polymer selected from polyaniline, polypyrrole,polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g.sulfonated versions), or a combination thereof.

In some embodiments, the sulfonated elastomer composite may form amixture, blend, or semi-IPN with a lithium ion-conducting polymerselected from poly(ethylene oxide) (PEO), polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVDF), poly bis-methoxyethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonatedderivative thereof, or a combination thereof. Sulfonation is hereinfound to impart improved lithium ion conductivity to a polymer.

The cathode active material may be selected from an inorganic material,an organic material, a polymeric material, or a combination thereof. Theinorganic material may be selected from a metal oxide, metal phosphate,metal silicide, metal selenide, metal sulfide, or a combination thereof.

The inorganic material may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, or a combination thereof.

In certain preferred embodiments, the inorganic material is selectedfrom a metal fluoride or metal chloride including the group consistingof CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂,AgF, CuCl₂, FeCl₃, MnCl₂, and combinations thereof. In certain preferredembodiments, the inorganic material is selected from a lithiumtransition metal silicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄,wherein M and Ma are selected from Fe, Mn, Co, Ni, V, or VO; Mb isselected from Fe, Mn, Co, Ni, V, Ti, Al, B, Sn, or Bi; and x+y≤1.

In certain preferred embodiments, the inorganic material is selectedfrom a transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof. The inorganic material isselected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, avanadium oxide, or a combination thereof.

The cathode active material layer may contain a metal oxide containingvanadium oxide selected from the group consisting of VO₂, Li_(x)VO₂,V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃,Li_(x)V₆O₁₃, their doped versions, their derivatives, and combinationsthereof, wherein 0.1<x<5.

The cathode active material layer may contain a metal oxide or metalphosphate, selected from a layered compound LiMO₂, spinel compoundLiM₂O₄, olivine compound LiMPO₄, silicate compound Li₂MSiO₄, tavoritecompound LiMPO₄F, borate compound LiMBO₃, or a combination thereof,wherein M is a transition metal or a mixture of multiple transitionmetals.

In some embodiments, the inorganic material is selected from: (a)bismuth selenide or bismuth telluride, (b) transition metaldichalcogenide or trichalcogenide, (c) sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, cobalt, manganese, iron, nickel, or a transition metal; (d)boron nitride, or (e) a combination thereof.

The cathode active material layer may contain an organic material orpolymeric material selected from poly(anthraquinonyl sulfide) (PAQS), alithium oxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.

The thioether polymer is selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In other embodiments, the cathode active material layer contains anorganic material selected from a phthalocyanine compound, such as copperphthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, or acombination thereof.

The cathode active material is preferably in a form of nanoparticle(spherical, ellipsoidal, and irregular shape), nanowire, nanofiber,nanotube, nanosheet, nanobelt, nanoribbon, nanodisc, nanoplatelet, ornanohorn having a thickness or diameter less than 100 nm. These shapescan be collectively referred to as “particles” unless otherwisespecified or unless a specific type among the above species is desired.Further preferably, the cathode active material has a dimension lessthan 50 nm, even more preferably less than 20 nm, and most preferablyless than 10 nm. In some embodiments, one particle or a cluster ofparticles may be coated with or embraced by a layer of carbon disposedbetween the particle(s) and/or a sulfonated elastomer composite layer(an encapsulating shell).

The cathode layer may further contain a graphite, graphene, or carbonmaterial mixed with the cathode active material particles. The carbon orgraphite material is selected from polymeric carbon, amorphous carbon,chemical vapor deposition carbon, coal tar pitch, petroleum pitch,mesophase pitch, carbon black, coke, acetylene black, activated carbon,fine expanded graphite particle with a dimension smaller than 100 nm,artificial graphite particle, natural graphite particle, or acombination thereof. Graphene may be selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenatedgraphene, nitrogenated graphene, functionalized graphene, etc.

The cathode active material particles may be coated with or embraced bya conductive protective coating, selected from a carbon material,graphene, electronically conductive polymer, conductive metal oxide, orconductive metal coating. Preferably, the cathode active material, inthe form of a nanoparticle, nanowire, nanofiber, nanotube, nanosheet,nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn ispre-intercalated or pre-doped with lithium ions to form a prelithiatedanode active material having an amount of lithium from 0.1% to 54.7% byweight of said prelithiated anode active material.

The present invention also provides a lithium metal-air batterycomprising an air cathode, an anode comprising a sulfonated elastomercomposite based protective layer as defined above, and electrolyte, orelectrolyte combined with a separator, disposed between the anode andthe air cathode. In the air cathode, oxygen from the open air (or froman oxygen supplier external to the battery) is the primary cathodeactive material. The air cathode needs an inert material to support thelithium oxide material formed at the cathode. The applicants havesurprisingly found that an integrated structure of conductivenanofilaments can be used as an air cathode intended for supporting thedischarge product (e.g., lithium oxide).

Hence, a further embodiment of the present invention is a lithiummetal-air battery, wherein the air cathode comprises an integratedstructure of electrically conductive nanometer-scaled filaments that areinterconnected to form a porous network of electron-conducting pathscomprising interconnected pores, wherein the filaments have a transversedimension less than 500 nm (preferably less than 100 nm). Thesenanofilaments can be selected from carbon nanotubes (CNTs), carbonnanofibers (CNFs), graphene sheets, carbon fibers, graphite fibers, etc.

The invention also provides a method of manufacturing a lithium battery,the method comprising: (a) providing a cathode active material layer andan optional cathode current collector to support the cathode activematerial layer; (b) providing an anode active material layer (containinga lithium metal or lithium alloy foil or coating) and an optional anodecurrent collector to support the lithium metal or lithium alloy foil orcoating; (c) providing an electrolyte in contact with the anode activematerial layer and the cathode active material layer and an optionalseparator electrically separating the anode and the cathode; and (d)providing an anode-protecting layer of a sulfonated elastomer compositehaving a recoverable tensile elastic strain from 2% to 800% (preferablyfrom 5% to 300%), a lithium ion conductivity no less than 10⁻⁶ S/cm atroom temperature, and a thickness from 1 nm to 100 μm (preferably from10 nm to 10 μm). This anode-protecting layer is disposed between thelithium metal or lithium alloy foil or coating and the porous separator(or solid-state electrolyte).

The invention also provides a method of improving the cycle-life of alithium metal secondary battery (not including a lithium-sulfur batteryor lithium-selenium battery). The method comprises implementing ananode-protecting layer between an anode active material layer and aporous separator/electrolyte, wherein the anode-protecting layercomprises a conductive sulfonated elastomer composite having from 0.01%to 50% by weight of a conductive reinforcement material dispersed in asulfonated elastomeric matrix material and the layer of conductivesulfonated elastomer composite has a thickness from 1 nm to 100 μm, afully recoverable tensile strain from 2% to 500%, a lithium ionconductivity from 10⁻⁷ S/cm to 5×10⁻² S/cm, and an electricalconductivity from 10⁻⁷ S/cm to 100 S/cm when measured at roomtemperature. Basically, this protecting layer is bothelectron-conducting and lithium ion-conducting.

In some embodiments, the conductive reinforcement material used in themethod is selected from graphene sheets, carbon nanotubes, carbonnanofibers, carbon or graphite fibers, expanded graphite flakes, metalnanowires, conductive polymer fibers, or a combination thereof.

In some embodiments, the sulfonated elastomeric matrix material containsa material selected from a sulfonated version of natural polyisoprene,synthetic polyisoprene, polybutadiene, chloroprene rubber,polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber,ethylene propylene rubber, ethylene propylene diene rubber,metallocene-based poly(ethylene-co-octene) elastomer,poly(ethylene-co-butene) elastomer, styrene-ethyl ene-butadiene-styreneelastomer, epichlorohydrin rubber, polyacrylic rubber, silicone rubber,fluorosilicone rubber, perfluoroelastomers, polyether block amides,chlorosulfonated polyethylene, ethylene-vinyl acetate, thermoplasticelastomer, protein resilin, protein elastin, ethyleneoxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer,or a combination thereof.

In the above-defined method, the step of implementing ananode-protecting layer is conducted by depositing a layer of asulfonated elastomer composite onto one primary surface of the anodeactive material layer to form a protected anode, optionally compressingthe protected anode to improve a contact between the anode-protectinglayer and the anode active material layer, followed by combining theprotected anode, the separator/electrolyte, and the cathode together toform the lithium metal secondary battery. A good contact between theanode active material layer and the anode-protecting layer is essential.

In certain embodiments, the step of implementing an anode-protectinglayer is conducted by depositing a layer of first sulfonated elastomercomposite onto one primary surface of the separator to form a coatedseparator, followed by combining the anode, the coated separator, thecathode, and the electrolyte together to form the lithium metalsecondary battery. A compressive stress may be advantageously applied(e.g. via press-rolling) to improve the contact between theanode-protecting layer and the anode active material layer to beprotected.

In certain embodiments, the step of implementing an anode-protectinglayer is conducted by forming a layer of a sulfonated elastomercomposite, followed by laminating the anode layer, the layer ofsulfonated elastomer composite, the separator layer, the cathode layer,along with the electrolyte to form the lithium metal secondary battery,wherein an optional (but desirable) compressive stress is applied toimprove the contact between the anode-protecting layer and the anodeactive material layer during or after this laminating step.

Preferably, the sulfonated elastomer composite has a lithium-ionconductivity from 10⁻⁵ S/cm to 5×10⁻² S/cm. In some embodiments, thesulfonated elastomer composite has a recoverable tensile strain from 10%to 300% (more preferably >30%, and further more preferably >50%).

In certain embodiments, the procedure of providing a sulfonatedelastomer composite contains providing a mixture/blend/composite of asulfonated elastomer with an electronically conductive polymer (e.g.polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer,a sulfonated derivative thereof, or a combination thereof), alithium-ion conducting material, a reinforcement material (e.g. carbonnanotube, carbon nanofiber, and/or graphene), or a combination thereof.

In this mixture/blend/composite, the lithium ion-conducting material isdispersed in the sulfonated elastomer composite and is preferablyselected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or a combination thereof,wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1 and 1≤y≤4.

In some embodiments, the lithium ion-conducting material is dispersed inthe sulfonated elastomer composite and is selected from lithiumperchlorate (LiClO₄), lithium hexafluorophosphate (LiPF₆), lithiumborofluoride (LiBF₄), lithium hexafluoroarsenide (LiAsF₆), lithiumtrifluoro-methanesulfonate (LiCF₃SO₃), bis-trifluoromethyl sulfonylimidelithium (LiN(CF₃SO₂)₂), lithium bis(oxalato)borate (LiBOB), lithiumoxalyldifluoroborate (LiBF₂C₂O₄), lithium nitrate (LiNO₃),Li-fluoroalkyl-phosphate (LiPF₃(CF₂CF₃)₃), lithiumbisperfluoro-ethylsulfonylimide (LiBETI), lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, or a combination thereof.

The anode-protecting layer implemented between the anode active layerand the separator (or the solid-state electrolyte) is mainly for thepurpose of reducing or eliminating the lithium metal dendrite byproviding a more stable Li metal-electrolyte interface that is moreconducive to uniform deposition of Li metal during battery charges. Thisanode-protecting layer also acts to block the penetration of anydendrite, if initiated, from reaching the separator or cathode. Thisanode-protecting layer, being highly elastic, also can shrink or expandsresponsive to the thickness increase or decrease of the anode activematerial layer. Other advantages will become more transparent later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic of a prior art lithium metal battery cell, containingan anode layer (a thin Li foil or Li coating deposited on a surface of acurrent collector, Cu foil), a porous separator, and a cathode activematerial layer, which is composed of particles of a cathode activematerial, a conductive additive (not shown) and a resin binder (notshown). A cathode current collector supporting the cathode active layeris also shown.

FIG. 2 Schematic of a presently invented lithium metal battery cellcontaining an anode layer (a thin Li foil or Li coating deposited on asurface of a current collector, Cu foil), a sulfonated elastomercomposite-based anode-protecting layer, a porous separator/electrolytelayer (or a layer of solid-state electrolyte), and a cathode activematerial layer, which is composed of particles of a cathode activematerial, a conductive additive (not shown) and a resin binder (notshown). A cathode current collector supporting the cathode active layeris also shown.

FIG. 3 The specific intercalation capacity curves of four lithium cells:2 cells each having a cathode containing V₂O₅ particles (one cell havingan anode-protecting layer and the other not) and 2 cells each having acathode containing graphene-embraced V₂O₅ particles (one cell having arotaxane polymer-based protective layer and the other not).

FIG. 4 The specific capacity values of two lithium-LiCoO₂ cells(initially the cell being lithium-free) featuring (1) high-elasticitysulfonated elastomer composite layer at the anode and (2) no protectionlayer at the anode, respectively.

FIG. 5 The discharge capacity curves of two coin cells having aFeF₃-based of cathode active materials: (1) having a high-elasticitysulfonated elastomer composite-protected anode; and (2) noanode-protecting layer.

FIG. 6 Specific capacities of two lithium-FePc (organic) cells, eachhaving Li foil as an anode active material and FePc/RGO mixtureparticles as the cathode active material (one cell containing asulfonated elastomer composite-protected anode and the other no anodeprotection layer).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is directed at a lithium metal secondary battery, whichis preferably based on an organic electrolyte, a polymer gelelectrolyte, an ionic liquid electrolyte, a quasi-solid electrolyte, ora solid-state electrolyte. The shape of a lithium metal secondarybattery can be cylindrical, square, button-like, etc. The presentinvention is not limited to any battery shape or configuration or anytype of electrolyte. The invented lithium secondary battery does notinclude a lithium-sulfur cell or lithium-selenium cell.

The invention provides a lithium metal secondary battery, comprising acathode, an anode, and electrolyte (e.g. solid-state electrolyte) orseparator-electrolyte assembly (porous separator and liquid electrolyte,gel electrolyte, quasi-solid electrolyte, etc.) disposed between thecathode and the anode, wherein the anode comprises: (a) a lithium metallayer (e.g. particles, foil or coating of lithium or lithium alloy) asan anode active material layer or electrode; and (b) a thin layer of aconductive sulfonated elastomer composite (anode-protecting layer)having from 0.01% to 40% by weight of a conductive reinforcementmaterial and from 0.01% to 40% by weight of an electrochemically stableinorganic filler dispersed in a sulfonated elastomeric matrix materialand this layer of conductive sulfonated elastomer composite has athickness from 1 nm to 100 μm, a fully recoverable tensile strain from2% to 500%, a lithium ion conductivity from 10⁻⁷ S/cm to 5×10⁻² S/cm,and an electrical conductivity from 10⁻⁷ S/cm to 100 S/cm when measuredat room temperature. The sulfonated elastomer composite is a separateand discrete layer (separate from and in addition to the anode activematerial layer) that is disposed (interposed) between the lithium metallayer and the porous separator (or solid-state electrolyte). The foil orcoating of lithium or lithium alloy may be supported by a currentcollector (e.g. a Cu foil, a Ni foam, a porous layer of nanofilaments,such as graphene sheets, carbon nanofibers, carbon nanotubes, etc.forming a 3D interconnected network of electron-conducting pathways).

Preferably, the sulfonated elastomer composite layer has a lithium ionconductivity no less than 10⁻⁶ S/cm (typically from 10⁻⁵ S/cm to 5×10⁻²S/cm, measured at room temperature), and a thickness from 10 nm to 20μm.

In some embodiments, the sulfonated elastomer composite has from 0.01%to 40% by weight (based on the total weight of the sulfonated elastomercomposite) of a conductive reinforcement material dispersed in asulfonated elastomeric matrix material, wherein the conductivereinforcement material is selected from graphene sheets, carbonnanotubes, carbon nanofibers, metal nanowires, conductive polymerfibers, or a combination thereof.

The conducting reinforcement material is preferably in a filamentary orsheet-like form, such as a nanotube, nanofiber, nanowire, nanoplatelet,or nanodisc. In some embodiments, the conductive reinforcement materialis selected from graphene sheets, carbon nanotubes, carbon nanofibers,carbon or graphite fibers, expanded graphite flakes, metal nanowires,conductive polymer fibers, or a combination thereof. These areelectron-conducting materials and the sulfonated elastomer matrix is alithium ion- and sodium ion-conducting material. By combining such asulfonated elastomer and a conducting reinforcement (0-40% by weight,preferably 0.1%-30%, and more preferably 0.1-15%), one obtains acomposite that is both electron conducting and ion-conducting andcapable of allowing electrons and lithium ions to migrate in and out ofthe particulate without much resistance.

The graphene sheets to be dispersed in a sulfonated elastomer matrix arepreferably selected from pristine graphene, graphene oxide, reducedgraphene oxide, graphene fluoride, graphene chloride, nitrogenatedgraphene, hydrogenated graphene, doped graphene, functionalizedgraphene, or a combination thereof. The graphene sheets preferablycomprise single-layer graphene or few-layer graphene, wherein thefew-layer graphene is defined as a graphene platelet formed of less than10 graphene planes. The carbon nanotubes (CNTs) can be a single-walledCNT or multi-walled CNT. The carbon nanofibers may be vapor-grown carbonnanofibers or electrospinning based carbon nanofibers (e.g. electrospunpolymer nanofibers that are subsequently carbonized).

Preferably, the sulfonated elastomeric matrix material contains asulfonated version of an elastomer selected from natural polyisoprene,synthetic polyisoprene, polybutadiene, chloroprene rubber,polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber,ethylene propylene rubber, ethylene propylene diene rubber,metallocene-based poly(ethylene-co-octene) (POE) elastomer,poly(ethylene-co-butene) (PBE) elastomer,styrene-ethylene-butadiene-styrene (SEBS) elastomer, epichlorohydrinrubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber,perfluoroelastomers, polyether block amides, chlorosulfonatedpolyethylene, ethylene-vinyl acetate, thermoplastic elastomer, proteinresilin, protein elastin, ethylene oxide-epichlorohydrin copolymer,polyurethane, urethane-urea copolymer, or a combination thereof.

In certain embodiments, the inorganic filler for reinforcing theelastomer matrix may be selected from an oxide, carbide, boride,nitride, sulfide, phosphide, or selenide of a transition metal, alithiated version thereof, or a combination thereof. Preferably, thetransition metal is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y,Zr, Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, a combination thereof, ora combination thereof with Al, Ga, In, Sn, Pb, Sb, or Bi.

These inorganic fillers for reinforcing the elastomer shell arepreferably selected to have an intercalation potential (theelectrochemical potential at which lithium intercalates into thesematerials) higher than the intercalation potential of the activematerial encapsulated in the particulate. For instance, lithiumintercalates into Si at approximately 0.4-0.5 V (vs. Li/Li⁺) and theintercalation potential of lithium titanate (Li₄Ti₅O₁₂) is 1.1-1.5 V.The lithium titanate may be considered as a lithiated version oftitanium oxide (TiO₂), which has a lithium intercalation potential >2.5V. The inorganic filler must have a lithium intercalation potentialhigher than 1.1 V versus Li/Li⁺, preferably higher than 1.2 V, morepreferably higher than 1.4 V, and most preferably higher than 1.5 V.These electrochemical potential conditions are found to be surprisinglycapable of avoiding the formation of SEI on/in the encapsulating shelland preventing repeated formation and breakage of SEI on active materialparticles, which otherwise would result in continued and rapid decay ofbattery capacity.

Other examples of metal oxide are NbO₂ and its lithiated version andtitanium-niobium composite oxide (e.g. represented by a general formulaTiNb₂O₇) and its lithiated versions. They typically have a lithiumintercalation potential higher than 1.1 V versus Li/Li⁺.

The niobium-containing composite metal oxide for use as an inorganicfiller in the encapsulating elastomer shell may be selected from thegroup consisting of TiNb₂O₇, Li_(x)TiNb₂O₇ (0≤x≤5),Li_(x)M_((1-y))Nb_(y)Nb₂O_((7+δ)) (wherein 0≤x≤6, 0≤y≤1, −1≤δ≤1, andM=Ti or Zr), Ti_(x)Nb_(y)O₇ (0.5≤y/x<2.0), TiNb_(x)O_((2+5x/2))(1.9≤x<2.0), M_(x)Ti_((1-2x))Nb_((2+x))O_((7+δ)) (wherein 0≤x≤0.2,−0.3≤δ≤0.3, and M=a trivalent metal selected from Fe, Ga, Mo, Ta, V, Al,B, and a mixture thereof), M_(x)Ti_((2-2x))Nb_((10+x))O_((29+δ))(wherein 0≤x≤0.4, −0.3≤δ≤0.3, and M=a trivalent metal selected from Fe,Ga, Mo, Al, B, and a mixture thereof), M_(x)TiNb₂O₇ (x<0.5, and M=B, Na,Mg, Al, Si, S, P, K, Ca, Mo, W, Cr, Mn, Co, Ni, and Fe),TiNb_(2-x)Ta_(x)O_(y) (0≤x<2, 7≤y≤10), Ti₂Nb_(10-v)Ta_(v)O_(w) (0≤v<2,27≤y≤29), Li_(x)Ti_((1-y))M1_(y)Nb_((2-z))M2_(z)O_((7+δ)) (wherein0≤x≤5, 0≤y≤1, 0≤z≤2, −0.3≤δ≤0.3, M1=Zr, Si, and Sn, and M2=V, Ta, andBi), P-doped versions thereof, B-doped versions thereof, carbon-coatedversions thereof, and combinations thereof. In such a niobium-containingcomposite metal oxide, niobium oxide typically forms the main frameworkor backbone of the crystal structure, along with at least a transitionmetal oxide.

Transition metal oxide is but one of the many suitable inorganic fillermaterials for reinforcing the elastomer matrix. The inorganic filler maybe selected from an oxide, carbide, boride, nitride, sulfide, phosphide,or selenide of a transition metal, a lithiated version thereof, or acombination thereof. Preferably, these and other inorganic fillers arein a form of nanoparticle, nanowire, nanofiber, nanotube, nanosheet,nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn having adimension (diameter, thickness, or width, etc.) less than 100 nm,preferably less than 10 nm. These inorganic filler materials typicallyhave a lithium intercalation potential from 1.1 V to 4.5 V versusLi/Li⁺, and more typically and preferably from 1.1 V to 3.5 V, and mostpreferably from 1.1 V to 1.5 V. The lithium intercalation potential of afiller dispersed in the elastomeric matrix material may be higher thanthe lithium intercalation potential of the active material encapsulatedby the filled elastomer.

The inorganic filler material for reinforcing an elastomer matrixmaterial may also be selected from nanodiscs, nanoplatelets, ornanosheets (having a thickness from 1 nm to 100 nm) of: (a) bismuthselenide or bismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,nickel, manganese, or any transition metal; (d) boron nitride, or (e) acombination thereof. These nanodiscs, nanoplatelets, or nanosheetspreferably have a thickness less than 20 nm, more preferably from 1 nmto 10 nm.

Preferably, this anode-protecting layer is different in composition thanthe electrolyte per se used in the lithium battery and maintains as adiscrete layer (not to be dissolved in the electrolyte) that is disposedbetween the anode active material layer (e.g. Li foil or Li coating on acurrent collector) and the electrolyte (or electrolyte-separator layer).The anode-protecting layer may contain a liquid electrolyte thatpermeates or impregnates into the sulfonated elastomer composite.

We have discovered that this protective layer provides severalunexpected benefits: (a) the formation of dendrite has been essentiallyeliminated; (b) uniform deposition of lithium back to the anode side isreadily achieved; (c) the layer ensures smooth and uninterruptedtransport of lithium ions from/to the lithium foil/coating and throughthe interface between the lithium foil/coating and the protective layerwith minimal interfacial resistance; and (d) cycle stability can besignificantly improved and cycle life increased.

In a conventional lithium metal cell, as illustrated in FIG. 1, theanode active material (lithium) is deposited in a thin film form or athin foil form directly onto an anode current collector (e.g. a Cufoil). The battery is a lithium metal battery, lithium sulfur battery,lithium-air battery, lithium-selenium battery, etc. As previouslydiscussed in the Background section, these lithium secondary batterieshave the dendrite-induced internal shorting and “dead lithium” issues atthe anode.

We have solved these challenging issues that have troubled batterydesigners and electrochemists alike for more than 30 years by developingand implementing a new anode-protecting layer disposed between thelithium foil/coating and the separator layer. This protective layercomprises a sulfonated elastomer composite having a recoverable(elastic) tensile strain no less than 2% (preferably no less than 5%)under uniaxial tension and a lithium ion conductivity no less than 10⁻⁶S/cm at room temperature (preferably and more typically from 1×10⁻⁵ S/cmto 5×10⁻² S/cm). The sulfonated elastomer composite contains asulfonated elastomer composite network having a rotaxane structure or asulfonated elastomer composite structure at a crosslink point of saidsulfonated elastomer composite network.

As schematically shown in FIG. 2, one embodiment of the presentinvention is a lithium metal battery cell containing an anode layer (athin Li foil or Li coating deposited on a surface of a currentcollector, Cu foil), a sulfonated elastomer composite-basedanode-protecting layer, a porous separator, and a cathode activematerial layer, which is composed of particles of a cathode activematerial, a conductive additive (not shown) and a resin binder (notshown). A cathode current collector (e.g. Al foil) supporting thecathode active layer is also shown in FIG. 2. The lithium metal or alloyin the anode may be in a form of particles (e.g. surface-protected orsurface-stabilized particles of Li or Li alloy).

Sulfonated elastomer composite exhibits an elastic deformation of atleast 2% when measured under uniaxial tension. In the field of materialsscience and engineering, the “elastic deformation” is defined as adeformation of a material (when being mechanically stressed) that isessentially fully recoverable upon release of the load and the recoveryis essentially instantaneous. The elastic deformation is preferablygreater than 5%, more preferably greater than 10%, further morepreferably greater than 30%, and still more preferably greater than 100%but less than 500%.

It may be noted that although FIG. 2 shows a lithium coatingpre-existing at the anode when the lithium battery is made, this is butone embodiment of the instant invention. An alternative embodiment is alithium battery that does not contain a lithium foil or lithium coatingat the anode (only an anode current collector, such as a Cu foil or agraphene/CNT mat) when the battery is made. The needed lithium to bebounced back and forth between the anode and the cathode is initiallystored in the cathode active material (e.g. lithium vanadium oxideLi_(x)V₂O₅, instead of vanadium oxide, V₂O₅; or lithium transition metaloxide or phosphate, instead of, say, MoS₂). During the first chargingprocedure of the lithium battery (e.g. as part of the electrochemicalformation process), lithium comes out of the cathode active material,migrates to the anode side, and deposits on the anode current collector.The presence of the presently invented sulfonated elastomer compositelayer enables uniform deposition of lithium ions on the anode currentcollector surface. Such an alternative battery configuration avoids theneed to have a layer of lithium foil or coating being present duringbattery fabrication. Bare lithium metal is highly sensitive to airmoisture and oxygen and, thus, is more challenging to handle in a realbattery manufacturing environment. This strategy of pre-storing lithiumin the lithiated (lithium-containing) cathode active materials, such asLi_(x)V₂O₅ and Li₂S_(x), makes all the materials safe to handle in areal manufacturing environment. Cathode active materials, such asLi_(x)V₂O₅ and Li₂S_(x), are typically less air-sensitive.

The presently invented lithium secondary batteries can contain a widevariety of cathode active materials. The cathode active material layermay contain a cathode active material selected from an inorganicmaterial, an organic material, a polymeric material, or a combinationthereof. The inorganic material may be selected from a metal oxide,metal phosphate, metal silicide, metal selenide, transition metalsulfide, or a combination thereof.

The inorganic cathode active material may be selected from a lithiumcobalt oxide, lithium nickel oxide, lithium manganese oxide, lithiumvanadium oxide, lithium-mixed metal oxide, lithium iron phosphate,lithium manganese phosphate, lithium vanadium phosphate, lithium mixedmetal phosphate, lithium metal silicide, or a combination thereof.

In certain preferred embodiments, the inorganic material as a cathodeactive material for the lithium battery is selected from a metalfluoride or metal chloride including the group consisting of CoF₃, MnF₃,FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂, CuF, SnF₂, AgF, CuCl₂,FeCl₃, MnCl₂, and combinations thereof. In certain preferredembodiments, the inorganic material is selected from a lithiumtransition metal silicate, denoted as Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄,wherein M and Ma are selected from Fe, Mn, Co, Ni, V, or VO; Mb isselected from Fe, Mn, Co, Ni, V, Ti, Al, B, Sn, or Bi; and x+y<1.

In certain preferred embodiments, the inorganic material as a cathodeactive material is selected from a transition metal dichalcogenide, atransition metal trichalcogenide, or a combination thereof. Theinorganic material is selected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂,an iron oxide, a vanadium oxide, or a combination thereof.

The cathode active material layer may contain a metal oxide containingvanadium oxide selected from the group consisting of VO₂, Li_(x)VO₂,V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃,Li_(x)V₆O₁₃, their doped versions, their derivatives, and combinationsthereof, wherein 0.1<x<5.

The cathode active material layer may contain a metal oxide or metalphosphate, selected from a layered compound LiMO₂, spinel compoundLiM₂O₄, olivine compound LiMPO₄, silicate compound Li₂MSiO₄, tavoritecompound LiMPO₄F, borate compound LiMBO₃, or a combination thereof,wherein M is a transition metal or a mixture of multiple transitionmetals.

In some embodiments, the inorganic material is selected from: (a)bismuth selenide or bismuth telluride, (b) transition metaldichalcogenide or trichalcogenide, (c) sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, cobalt, manganese, iron, nickel, or a transition metal; (d)boron nitride, or (e) a combination thereof.

The cathode active material layer may contain an organic material orpolymeric material selected from poly(anthraquinonyl sulfide) (PAQS), alithium oxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.

The thioether polymer is selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In other embodiments, the cathode active material layer contains anorganic material selected from a phthalocyanine compound, such as copperphthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, or acombination thereof.

Preferably and typically, the sulfonated elastomer composite has alithium ion conductivity no less than 10⁻⁵ S/cm, more preferably no lessthan 10⁻⁴ S/cm, further preferably no less than 10⁻³ S/cm, and mostpreferably no less than 10⁻² S/cm. In some embodiments, the sulfonatedelastomer composite comprises from 0.1% to 50% (preferably 1% to 35%) byweight of a lithium ion-conducting additive dispersed in a sulfonatedelastomer composite matrix material. The sulfonated elastomer compositemust have a high elasticity (elastic deformation strain value >2%). Anelastic deformation is a deformation that is fully recoverable and therecovery process is essentially instantaneous (no significant timedelay). The sulfonated elastomer composite can exhibit an elasticdeformation from 2% up to 800% (8 times of its original length), moretypically from 5% to 500%, and further more typically from 10% to 300%,and most typically and desirably from 30% to 300%. It may be noted thatalthough a metal typically has a high ductility (i.e. can be extended toa large extent without breakage), the majority of the deformation isplastic deformation (non-recoverable) and only a small amount of elasticdeformation (typically <1% and more typically <0.2%).

Further, we have unexpectedly discovered that the presence of an amountof a lithium salt or sodium salt (1-35% by weight) and a liquid solvent(0-50%) can significantly increase the lithium-ion or sodium ionconductivity.

Typically, a sulfonated elastomer composite is originally in a monomeror oligomer states that can be cured to form a cross-linked polymer thatis highly elastic. Prior to curing, these polymers or oligomers aresoluble in an organic solvent to form a polymer solution. Anion-conducting or electron-conducting additive may be added to thissolution to form a suspension. This solution or suspension can then beformed into a thin layer of polymer precursor on a surface of an anodecurrent collector. The polymer precursor (monomer or oligomer andinitiator) is then polymerized and cured to form a lightly cross-linkedpolymer. This thin layer of polymer may be tentatively deposited on asolid substrate (e.g. surface of a polymer or glass), dried, andseparated from the substrate to become a free-standing polymer layer.This free-standing layer is then laid on a lithium foil/coating orimplemented between a lithium film/coating and electrolyte or separator.Polymer layer formation can be accomplished by using one of severalprocedures well-known in the art; e.g. spraying, spray-painting,printing, coating, extrusion-based film-forming, casting, etc.

One may dispense and deposit a layer of a sulfonated elastomer compositeonto a primary surface of the anode active material layer.Alternatively, one may dispense and deposit a layer of a sulfonatedelastomer composite onto a primary surface of a separator layer. Furtheralternatively, one may prepare separate free-standing discrete layers ofthe sulfonated elastomer composite first. This sulfonated elastomercomposite layer is then laminated together with the anode activematerial layer, separator/electrolyte, and the cathode layer to form abattery cell.

Sulfonation of an elastomer or rubber may be accomplished by exposingthe elastomer/rubber to a sulfonation agent in a solution state or meltstate, in a batch manner or in a continuous process. The sulfonatingagent may be selected from sulfuric acid, sulfonic acid, sulfurtrioxide, chlorosulfonic acid, a bisulfate, a sulfate (e.g. zincsulfate, acetyl sulfate, etc.), a mixture thereof, or a mixture thereofwith another chemical species (e.g. acetic anhydride, thiolacetic acid,or other types of acids, etc.). In addition to zinc sulfate, there are awide variety of metal sulfates that may be used as a sulfonating agent;e.g. those sulfates containing Mg, Ca, Co, Li, Ba, Na, Pb, Ni, Fe, Mn,K, Hg, Cr, and other transition metals, etc.

For instance, a triblock copolymer, poly(styrene-isobutylene-styrene) orSIBS, may be sulfonated to several different levels ranging from 0.36 to2.04 mequiv./g (13 to 82 mol % of styrene; styrene being 19 mol % of theunsulfonated block copolymer). Sulfonation of SIBS may be performed insolution with acetyl sulfate as the sulfonating agent. First, aceticanhydride reacts with sulfuric acid to form acetyl sulfate (asulfonating agent) and acetic acid (a by-product). Then, excess water isremoved since anhydrous conditions are required for sulfonation of SIBS.The SIBS is then mixed with the mixture of acetyl sulfate and aceticacid. Such a sulfonation reaction produces sulfonic acid substituted tothe para-position of the aromatic ring in the styrene block of thepolymer. Elastomers having an aromatic ring may be sulfonated in asimilar manner.

A sulfonated elastomer also may be synthesized by copolymerization of alow level of functionalized (i.e. sulfonated) monomer with anunsaturated monomer (e.g. olefinic monomer, isoprene monomer oroligomer, butadiene monomer or oligomer, etc.).

A broad array of elastomers can be sulfonated to become sulfonatedelastomers. The elastomeric material may be selected from naturalpolyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) andtrans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR forisoprene rubber), polybutadiene (BR for butadiene rubber), chloroprenerubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber(copolymer of isobutylene and isoprene, IIR), including halogenatedbutyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR),styrene-butadiene rubber (copolymer of styrene and butadiene, SBR),nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM(ethylene propylene rubber, a copolymer of ethylene and propylene), EPDMrubber (ethylene propylene diene rubber, a terpolymer of ethylene,propylene and a diene-component), epichlorohydrin rubber (ECO),polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ),fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such asViton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM:Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA),chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinylacetate (EVA), thermoplastic elastomers (TPE), protein resilin, proteinelastin, ethylene oxide-epichlorohydrin copolymer, polyurethane,urethane-urea copolymer, and combinations thereof.

In some embodiments, a sulfonated elastomer composite can form a polymermatrix composite containing a lithium ion-conducting additive dispersedin the sulfonated elastomer composite matrix material, wherein thelithium ion-conducting additive is selected from Li₂CO₃, Li₂O, Li₂C₂O₄,LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S,Li_(x)SO_(y), or a combination thereof, wherein X=F, Cl, I, or Br, R=ahydrocarbon group, 0<x≤1 and 1≤y≤4.

In some embodiments, the sulfonated elastomer composite can be mixedwith a lithium ion-conducting additive, which contains a lithium saltselected from lithium perchlorate (LiClO₄), lithium hexafluorophosphate(LiPF₆), lithium borofluoride (LiBF₄), lithium hexafluoroarsenide(LiAsF₆), lithium trifluoro-methanesulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂), lithiumbis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF₂C₂O₄),lithium nitrate (LiNO₃), Li-fluoroalkyl-phosphate (LiPF₃(CF₂CF₃)₃),lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, or a combination thereof.

The sulfonated elastomer composite may form a mixture, blend, orinterpenetrating network with an electron-conducting polymer selectedfrom polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclicpolymer, derivatives thereof (e.g. sulfonated versions), or acombination thereof. In some embodiments, the sulfonated elastomercomposite may form a mixture, co-polymer, or semi-interpenetratingnetwork with a lithium ion-conducting polymer selected frompoly(ethylene oxide) (PEO), polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVDF), poly bis-methoxyethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivativethereof (e.g. sulfonated versions), or a combination thereof.

The electrolyte for a lithium secondary cell may be an organicelectrolyte, ionic liquid electrolyte, gel polymer electrolyte,solid-state electrolyte (e.g. polymer solid electrolyte or inorganicsolid electrolyte), quasi-solid electrolyte or a combination thereof.The electrolyte typically contains an alkali metal salt (lithium salt,sodium salt, and/or potassium salt) dissolved in a solvent.

The solvent may be selected from 1,3-dioxolane (DOL),1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether (TEGDME),poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutylether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylenecarbonate (EC), dimethyl carbonate (DMC), methylethyl carbonate (MEC),diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylenecarbonate (PC), gamma-butyrolactone (γ-BL), acetonitrile (AN), ethylacetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene,methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate(VC), allyl ethyl carbonate (AEC), a hydrofluoroether, a roomtemperature ionic liquid solvent, or a combination thereof.

The electrolytic salts to be incorporated into a non-aqueous electrolytemay be selected from a lithium salt such as lithium perchlorate(LiClO₄), lithium hexafluorophosphate (LiPF₆), lithium borofluoride(LiBF₄), lithium hexafluoroarsenide (LiAsF₆), lithiumtrifluoro-metasulfonate (LiCF₃SO₃), bis-trifluoromethyl sulfonylimidelithium (LiN(CF₃SO₂)₂), lithium bis(oxalato)borate (LiBOB), lithiumoxalyldifluoroborate (LiBF₂C₂O₄), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium nitrate (LiNO₃), Li-fluoroalkyl-Phosphates(LiPF3(CF₂CF₃)₃), lithium bisperfluoroethysulfonylimide (LiBETI), anionic liquid salt, sodium perchlorate (NaClO₄), potassium perchlorate(KClO₄), sodium hexafluorophosphate (NaPF₆), potassiumhexafluorophosphate (KPF₆), sodium borofluoride (NaBF₄), potassiumborofluoride (KBF₄), sodium hexafluoroarsenide, potassiumhexafluoroarsenide, sodium trifluoro-metasulfonate (NaCF₃SO₃), potassiumtrifluoro-metasulfonate (KCF₃SO₃), bis-trifluoromethyl sulfonylimidesodium (NaN(CF₃SO₂)₂), sodium trifluoromethanesulfonimide (NaTFSI), andbis-trifluoromethyl sulfonylimide potassium (KN(CF₃SO₂)₂). Among them,LiPF₆, LiBF₄ and LiN(CF₃SO₂)₂ are preferred for Li—S cells, NaPF₆ andLiBF₄ for Na—S cells, and KBF₄ for K—S cells. The content ofaforementioned electrolytic salts in the non-aqueous solvent ispreferably 0.5 to 3.0 M (mol/L) at the cathode side and 3.0 to >10 M atthe anode side.

The ionic liquid is composed of ions only. Ionic liquids are low meltingtemperature salts that are in a molten or liquid state when above adesired temperature. For instance, a salt is considered as an ionicliquid if its melting point is below 100° C. If the melting temperatureis equal to or lower than room temperature (25° C.), the salt isreferred to as a room temperature ionic liquid (RTIL). The IL salts arecharacterized by weak interactions, due to the combination of a largecation and a charge-delocalized anion. This results in a low tendency tocrystallize due to flexibility (anion) and asymmetry (cation).

A typical and well-known ionic liquid is formed by the combination of a1-ethyl-3-methylimidazolium (EMI) cation and anN,N-bis(trifluoromethane)sulfonamide (TFSI) anion. This combinationgives a fluid with an ionic conductivity comparable to many organicelectrolyte solutions and a low decomposition propensity and low vaporpressure up to −300-400° C. This implies a generally low volatility andnon-flammability and, hence, a much safer electrolyte for batteries.

Ionic liquids are basically composed of organic ions that come in anessentially unlimited number of structural variations owing to thepreparation ease of a large variety of their components. Thus, variouskinds of salts can be used to design the ionic liquid that has thedesired properties for a given application. These include, among others,imidazolium, pyrrolidinium and quaternary ammonium salts as cations andbis(trifluoromethanesulfonyl) imide, bis(fluorosulfonyl)imide, andhexafluorophosphate as anions. Based on their compositions, ionicliquids come in different classes that basically include aprotic, proticand zwitterionic types, each one suitable for a specific application.

Common cations of room temperature ionic liquids (RTILs) include, butnot limited to, tetraalkylammonium, di-, tri-, andtetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium,dialkylpiperidinium, tetraalkylphosphonium, and trialkylsulfonium.Common anions of RTILs include, but not limited to, BF₄ ⁻, B(CN)₄ ⁻,CH₃BF₃ ⁻, CH2CHBF₃ ⁻, CF₃BF₃ ⁻, C₂F₅BF₃ ⁻, n-C₃F₇BF₃ ⁻, n-C₄F₉BF₃ ⁻, PF₆⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, N(COCF₃)(SO₂CF₃)⁻, N(SO₂F)₂ ⁻,N(CN)₂ ⁻, C(CN)₃ ⁻, SCN⁻, SeCN⁻, CuCl₂ ⁻, AlCl₄ ⁻, F(HF)_(2.3) ⁻, etc.Relatively speaking, the combination of imidazolium- or sulfonium-basedcations and complex halide anions such as AlCl₄ ⁻, BF₄ ⁻, CF₃CO₂ ⁻,CF₃SO₃ ⁻, NTf₂ ⁻, N(SO₂F)₂ ⁻, or F(HF)_(2.3) ⁻ results in RTILs withgood working conductivities.

RTILs can possess archetypical properties such as high intrinsic ionicconductivity, high thermal stability, low volatility, low (practicallyzero) vapor pressure, non-flammability, the ability to remain liquid ata wide range of temperatures above and below room temperature, highpolarity, high viscosity, and wide electrochemical windows. Theseproperties, except for the high viscosity, are desirable attributes whenit comes to using an RTIL as an electrolyte ingredient (a salt and/or asolvent) in a lithium metal cell.

Example 1: Sol-Gel Process for Producing Li_(x)Tinb₂O₇ (TNO) as aReinforcement or Filler for the Elastomer-Based Anode-Protecting Layer

The synthesis method involves precipitating the precursor toniobium-based composite metal oxide nanoparticles from a solutionreactant mixture of Nb(OH)₅ (dissolved in citric acid) and water-ethanolsolution containing Ti(OC₃H₇)₄. Specifically, Nb₂O₅ was dissolved inhydrofluoric acid to form a transparent solution. In order to remove theF ions from the solution, ammonia was added to obtain a white Nb(OH)₅precipitate. After the precipitate was washed and dried, the Nb(OH)₅ wasdissolved in citric acid to form a Nb(V)-citrate solution. Awater-ethanol solution containing Ti(OC₃H₇)₄ was added to this solutionwhile the pH value of the solution was adjusted using ammonia. Thisfinal mixture containing Nb(V) and Ti(IV) ions was then stirred at 90°C. to form a citric gel. This gel was then heated to 140° C. to obtain aprecursor, which was annealed at 900° C. and at 1350° C. to obtain theLi_(x)TiNb₂O₇ (TNO) powder.

The powder was ball-milled in a high-intensity ball mill to obtainnanoparticles of TNO, which were then dispersed in monomers/oligomers ofseveral different elastomers (e.g. polyurethane, polybutadine, etc.) toform reacting suspensions. The monomers/oligomers were then polymerizedto a controlled extent without allowing for any significantcross-linking of chains. This procedure often enables chemical bondingbetween the elastomer and the metal oxide particles or other inorganicfiller species (particles of transition metal carbide, sulfide,selenide, phosphide, nitride, boride, etc.). These non-cured ornon-crosslinked polymers were then each separately dissolved in anorganic solvent to form a suspension (polymer-solvent solution plusbonded metal oxide particles and a selected conductive additive; e.g.graphene sheets). The slurry was then spray-deposited onto a lithiumanode layer or made into a thin film via coating/casting. The thin filmwas then laminated with a lithium metal layer, along with anelectrolyte/separator, and a cathode layer to form a lithium metalbattery cell.

Example 2: Preparation of TiNb₂O₇, TiMoNbO₇, and TiFe_(0.3)Nb_(1.7)O₇ asa Reinforcement or Filler for the Elastomer-Based Anode-Protecting Layer

A niobium-titanium composite oxide represented by the general formulaTiNb₂O₇ was synthesized, by following the following procedure:Commercially available niobium oxide (Nb₂O₅) and a titanate protoncompound were used as starting materials. The titanate proton compoundwas prepared by immersing potassium titanate in hydrochloric acid at 25°C. for 72 hours. In the process, 1M hydrochloric acid was replaced witha 1M of fresh acid every 24 hours. As a result, potassium ions wereexchanged for protons to obtain the titanate proton compound.

The niobium oxide (Nb₂O₅) and the titanate proton compound were weighedsuch that the molar ratio of niobium to titanium in the synthesizedcompound was 3. The mixture was dispersed in 100 ml of pure water,followed by vigorous mixing. The obtained mixture was placed in a heatresistant container and was subjected to hydrothermal synthesis underconditions of 180° C. for a total of 24 hours. The obtained sample waswashed in pure water three times, and then dried. The sample was thensubjected to a heat treatment at 1,100° C. for 24 hours to obtainTiNb₂O₇.

Additionally, a niobium-molybdenum-titanium composite oxide wassynthesized in the same manner as above except that niobium oxide(Nb₂O₅), molybdenum oxide (Mo₂O₅), and a titanate proton compound wereweighed such that the molar ratio of niobium to titanium and that ofmolybdenum to titanium in the synthesized compound was 1.5 and 1.5,respectively. As a result, a niobium-molybdenum-titanium composite oxide(TiMoNbO₇) was obtained.

In addition, a niobium-Iron-titanium composite oxide was synthesized inthe same manner as above except that niobium oxide (Nb₂O₅), a titanateproton compound, and iron oxide (Fe₂O₃) were weighed such that the molarratio of niobium to titanium and of iron to titanium in the synthesizedcompound was 3 and 0.3, respectively. As a result, a niobium-titaniumcomposite oxide (TiFe_(0.3)Nb_(1.7)O₇) was obtained.

The above niobium-containing composite metal oxide powders (TiNb₂O₇,TiMoNbO₇, and TiFe_(0.3)Nb_(1.7)O₇) were separately added into a monomerof synthetic polyisoprene and a mixture of monomers for urethane-ureacopolymer, respectively. Polymerization of the respective reacting masswas initiated and proceeded to obtain linear chains withoutcrosslinking. This step was found to create some bonding between thecomposite metal oxide particles. Subsequently, these substantiallylinear chains were dissolved in a solvent (e.g. benzene and DMAc) toform a solution and a desired amount of graphene sheets or CNTs wasadded to form a slurry. The slurry was then cast into thin films for useas an anode-protecting layer.

Example 3: Preparation of Ga_(0.1)Ti_(0.8)Nb_(2.1)O₇ as a Reinforcementor Filler for the Elastomer Layer

In an experiment, 0.125 g of GaCl₃ and 4.025 g of NbCl₅ were dissolvedin 10 mL of anhydrous ethanol under an inert atmosphere (argon) andmagnetic stirring. The solution was transferred under air. Then, addedto this solution was 6.052 g solution of titanium oxysulfate (TiOSO₄) at15% by mass in sulfuric acid, followed by 10 mL of ethanol to dissolvethe precursors under a magnetic stirring. The pH of the solution wasadjusted to 10 by slow addition of ammonia NH₃ at 28% by mass intowater.

The paste was transferred into a Teflon container having a 90-mLcapacity, which was then placed in an autoclave. The paste was thenheated up to 220° C. for 5 hours with a heating and cooling ramp of 2and 5 degrees C./min, respectively. The paste was then washed withdistilled water by centrifugation until a pH between 6 and 7 wasobtained. The resulting compound was heated at 60° C. for 12 hours andthen ball-milled for 30 min at 500 rpm (revolutions per minute) inhexane. After evaporation of the solvent, the powder was calcinated at950° C. for 1 hour with a heating/cooling ramp of 3 degrees C./min toproduce crystals of Ga_(0.1)Ti_(0.8)Nb_(2.1)O₇. These particles wereused as an inorganic filler to reinforce an elastomer matrix.

Example 4: Preparation of Fe_(0.1)Ti_(0.8)Nb_(2.1)O₇ Powder as aReinforcement for Elastomer

In a representative procedure, 0.116 g of FeCl₃ and 4.025 g of NbCl₅were dissolved in 10 mL of anhydrous ethanol under an inert atmosphere(argon) and magnetic stirring. The resulting solution was transferredunder air. Then, added to this solution was 6.052 g of titaniumoxysulfate (TiOSO₄) at 15% by mass in sulfuric acid and 10 mL of ethanolto dissolve the precursors under a magnetic stirring. The pH of thesolution was adjusted to 10 by slow addition of ammonia NH₃ at 28% bymass into water.

The paste was transferred into a Teflon container having a 90-mLcapacity, which was then placed in an autoclave. The paste was thenheated up to 220° C. for 5 hours with a heating and cooling ramp of 2and 5 degrees C./min, respectively. The paste was then washed withdistilled water by centrifugation until a pH between 6 and 7 wasobtained. The compound was heated at 60° C. for 12 hours and thenball-milled for 30 min at 500 rpm in hexane. After evaporation ofhexane, the powder was calcinated at 950° C. for 1 hour with aheating/cooling ramp of 3 degrees C./min to obtainFe_(0.1)Ti_(0.8)Nb_(2.1)O₇ crystals.

Example 5: Production of Molybdenum Diselenide Nanoplatelets (as aNanofiller) Using Direct Ultrasonication

A sequence of steps can be utilized to form nanoplatelets from manydifferent types of layered compounds: (a) dispersion of a layeredcompound in a low surface tension solvent or a mixture of water andsurfactant, (b) ultrasonication, and (c) an optional mechanical sheartreatment. For instance, dichalcogenides (MoSe₂) consisting of Se—Mo—Selayers held together by weak van der Waals forces can be exfoliated viathe direct ultrasonication process invented by our research group.Intercalation can be achieved by dispersing MoSe₂ powder in a siliconoil beaker, with the resulting suspension subjected to ultrasonicationat 120 W for two hours. The resulting MoSe₂ platelets were found to havea thickness in the range of approximately 1.4 nm to 13.5 nm with most ofthe platelets being mono-layers or double layers.

Other single-layer platelets of the form MX₂ (transition metaldichalcogenide), including MoS₂, TaS₂, ZrS₂, and WS₂, were similarlyexfoliated and separated. Again, most of the platelets were mono-layersor double layers when a high sonic wave intensity was utilized for asufficiently long ultrasonication time.

Example 6: Production of ZrS₂ Nanodiscs as a Nanofiller for theElastomer Layer

In a representative procedure, zirconium chloride (ZrCl₄) precursor (1.5mmol) and oleylamine (5.0 g, 18.7 mmol) were added to a 25-mL three-neckround-bottom flask under a protective argon atmosphere. The reactionmixture was first heated to 300° C. at a heating rate of 5° C./min underargon flow and subsequently CS₂ (0.3 mL, 5.0 mmol) was injected. After 1h, the reaction was stopped and cooled down to room temperature. Afteraddition of excess butanol and hexane mixtures (1:1 by volume), 18 nmZrS₂ nanodiscs (˜100 mg) were obtained by centrifugation. Larger sizednanodiscs ZrS₂ of 32 nm and 55 nm were obtained by changing reactiontime to 3 h and 6 h, respectively otherwise under identical conditions.

Example 7: Preparation of Boron Nitride Nanosheets as a Nanofiller forthe Elastomer Layer

Five grams of boron nitride (BN) powder, ground to approximately 20 μmor less in sizes, were dispersed in a strong polar solvent (dimethylformamide) to obtain a suspension. An ultrasonic energy level of 85 W(Branson 5450 Ultrasonicator) was used for exfoliation, separation, andsize reduction for a period of 1-3 hours. This is followed bycentrifugation to isolate the BN nanosheets. The BN nanosheets obtainedwere from 1 nm thick (<3 atomic layers) up to 7 nm thick.

Example 8: Sulfonation of Triblock CopolymerPoly(Styrene-Isobutylene-Styrene) or SIBS

An example of the sulfonation procedure used in this study is summarizedas follows: a 10% (w/v) solution of SIBS (50 g) and a desired amount ofgraphene oxide sheets (0.15% to 40.5% by wt.) in methylene chloride (500ml) was prepared. The solution was stirred and refluxed at approximately40 8C, while a specified amount of acetyl sulfate in methylene chloridewas slowly added to begin the sulfonation reaction. Acetyl sulfate inmethylene chloride was prepared prior to this reaction by cooling 150 mlof methylene chloride in an ice bath for approximately 10 min. Aspecified amount of acetic anhydride and sulfuric acid was then added tothe chilled methylene chloride under stirring conditions. Sulfuric acidwas added approximately 10 min after the addition of acetic anhydridewith acetic anhydride in excess of a 1:1 mole ratio. This solution wasthen allowed to return to room temperature before addition to thereaction vessel.

After approximately 5 h, the reaction was terminated by slowly adding100 ml of methanol. The reacted polymer solution was then precipitatedwith deionized water. The precipitate was washed several times withwater and methanol, separately, and then dried in a vacuum oven at 50°C. for 24 h. This washing and drying procedure was repeated until the pHof the wash water was neutral. After this process, the final polymeryield was approximately 98% on average. This sulfonation procedure wasrepeated with different amounts of acetyl sulfate to produce severalsulfonated polymers with various levels of sulfonation or ion-exchangecapacities (IECs). The mol % sulfonation is defined as: mol %=(moles ofsulfonic acid/moles of styrene)×100%, and the IEC is defined as themille-equivalents of sulfonic acid per gram of polymer (mequiv./g).

After sulfonation and washing of each polymer, the S-SIBS samples weredissolved in a mixed solvent of toluene/hexanol (85/15, w/w) withconcentrations ranging from 0.5 to 2.5% (w/v). Desired amounts ofgraphene sheets and inorganic additive, such as BN, ZrS₂ nanosheets, andTiMoNbO₇, (if not added at an earlier stage) were then added into thesolution to form slurry samples. The slurry samples were slot-die coatedon a PET plastic substrate to form layers of sulfonated elastomercomposite.

Example 9: Synthesis of Sulfonated Polybutadiene (PB) by Free RadicalAddition of Thiolacetic Acid (TAA) Followed by In Situ Oxidation withPerformic Acid

A representative procedure is given as follows. PB (8.0 g) was dissolvedin toluene (800 mL) under vigorous stirring for 72 h at room temperaturein a 1 L round-bottom flask. Benzophenone (BZP) (0.225 g; 1.23 mmol;BZP/olefin molar ratio=1:120) and TAA (11.9 mL; 0.163 mol, TAA/olefinmolar ratio=1.1) and a desired amount of graphene sheets (0.1%-40% bywt.) were introduced into the reactor, and the polymer solution wasirradiated for 1 h at room temperature with UV light of 365 nm and powerof 100 W.

The resulting thioacetylated polybutadiene (PB-TA)/graphene compositewas isolated by pouring 200 mL of the toluene solution in a plenty ofmethanol and the polymer recovered by filtration, washed with freshmethanol, and dried in vacuum at room temperature (Yield=3.54 g). Formicacid (117 mL; 3.06 mol; HCOOH/olefin molar ratio=25), along with adesired amount of anode active material particles, from 10 to 100 grams)were added to the toluene solution of PB-TA at 50° C. followed by slowaddition of 52.6 mL of hydrogen peroxide (35 wt %; 0.61 mol; H₂O₂/olefinmolar ratio=5) in 20 min. We would like to caution that the reaction isautocatalytic and strongly exothermic. The resulting slurry wasspray-dried to obtain sulfonated polybutadiene (PB-SA)/graphenecomposite layers.

It may be noted that graphene sheets may be added at different stages ofthe procedure: before, during or after BZP is added orbefore/during/after the inorganic filler is added.

Example 10: Synthesis of Sulfonated SBS

Sulfonated styrene-butadiene-styrene triblock copolymer (SBS) basedelastomer was directly synthesized. First, SBS (optionally along withgraphene sheets) is first epoxidized by performic acid formed in situ,followed by ring-opening reaction with an aqueous solution of NaHSO₃. Ina typical procedure, epoxidation of SBS was carried out via reaction ofSBS in cyclohexane solution (SBS concentration=11 g/100 mL) withperformic acid formed in situ from HCOOH and 30% aqueous H₂O₂ solutionat 70° C. for 4 h, using 1 wt % poly(ethylene glycol)/SBS as a phasetransfer catalyst. The molar ratio of H₂O₂/HCOOH was 1. The product(ESBS) was precipitated and washed several times with ethanol, followedby drying in a vacuum dryer at 60° C.

Subsequently, ESBS was first dissolved in toluene to form a solutionwith a concentration of 10 g/100 mL, into which was added 5 wt %TEAB/ESBS as a phase transfer catalyst and 5 wt % DMA/ESBS as aring-opening catalyst. Herein, TEAB=tetraethyl ammonium bromide andDMA=N,N-dimethyl aniline. An aqueous solution of NaHSO₃ and Na₂SO₃(optionally along with graphene sheets or CNTs, if not added earlier)was then added with vigorous stirring at 60° C. for 7 h at a molar ratioof NaHSO₃/epoxy group at 1.8 and a weight ratio of Na₂SO₃/NaHSO₃ at 36%.This reaction allows for opening of the epoxide ring and attaching ofthe sulfonate group according to the following reaction:

The reaction was terminated by adding a small amount of acetone solutioncontaining antioxidant. The mixture was washed with distilled water andthen precipitated by ethanol while being cast into thin films, followedby drying in a vacuum dryer at 50° C. It may be noted that graphenesheets (or CNTs, etc.) and the inorganic filler may be added duringvarious stages of the aforementioned procedure (e.g. right from thebeginning, or prior to the ring opening reaction).

Example 11: Synthesis of Sulfonated SBS by Free Radical Addition ofThiolacetic Acid (TAA) Followed by In Situ Oxidation with Per-FormicAcid

A representative procedure is given as follows. SBS (8.000 g) in toluene(800 mL) was left under vigorous stirring for 72 hours at roomtemperature and heated later on for 1 h at 65° C. in a 1 L round-bottomflask until the complete dissolution of the polymer. Thus, benzophenone(BZP, 0.173 g; 0.950 mmol; BZP/olefin molar ratio=1:132) and TAA (8.02mL; 0.114 mol, TAA/olefin molar ratio=1.1) were added, and the polymersolution was irradiated for 4 h at room temperature with UV light of 365nm and power of 100 W. To isolate a fraction of the thioacetylatedsample (S(B-TA)S), 20 mL of the polymer solution was treated with plentyof methanol, and the polymer was recovered by filtration, washed withfresh methanol, and dried in vacuum at room temperature. The toluenesolution containing the thioacetylated polymer was equilibrated at 50°C., and 107.4 mL of formic acid (2.84 mol; HCOOH/olefin molarratio=27.5) and 48.9 mL of hydrogen peroxide (35 wt %; 0.57 mol;H₂O₂/olefin molar ratio=5.5) were added in about 15 min. It may becautioned that the reaction is autocatalytic and strongly exothermic!The conductive reinforcement material was added before or after thisreaction. The resulting slurry was stirred for 1 h, and then most of thesolvent was distilled off in vacuum at 35° C. Finally, the slurrycontaining the sulfonated elastomer, along with desired additives, wasadded with acetonitrile, cast into films, washed with freshacetonitrile, and dried in vacuum at 35° C. to obtain layers ofsulfonated elastomers.

Other elastomers (e.g. polyisoprene, EPDM, EPR, polyurethane, etc.) weresulfonated in a similar manner. Alternatively, all the rubbers orelastomers can be directly immersed in a solution of sulfuric acid, amixture of sulfuric acid and acetyl sulfate, or other sulfonating agentdiscussed above to produce sulfonated elastomers/rubbers. Again,graphene sheets (or other conductive reinforcement material) andinorganic filler may be added at various stages of the procedure.

Example 12: Lithium Battery Containing a Sulfonated ElastomerComposite-Protected Lithium Anode and a Cathode Containing V₂O₅Particles

Cathode active material layers were prepared from V₂O₅ particles andgraphene-embraced V₂O₅ particles, respectively. The V₂O₅ particles werecommercially available. Graphene-embraced V₂O₅ particles were preparedin-house. In a typical experiment, vanadium pentoxide gels were obtainedby mixing V₂O₅ in a LiCl aqueous solution. The Lit exchanged gelsobtained by interaction with LiCl solution (the Li:V molar ratio waskept as 1:1) was mixed with a GO suspension and then placed in aTeflon-lined stainless steel 35 ml autoclave, sealed, and heated up to180° C. for 12 h. After such a hydrothermal treatment, the green solidswere collected, thoroughly washed, ultrasonicated for 2 minutes, anddried at 70° C. for 12 h followed by mixing with another 0.1% GO inwater, ultrasonicating to break down nanobelt sizes, and thenspray-drying at 200° C. to obtain graphene-embraced V₂O₅ compositeparticulates. Selected amounts of V₂O₅ particles and graphene-embracedV₂O₅ particles, respectively, were then each made into a cathode layerfollowing a well-known slurry coating process.

The sulfonated elastomer composite films for anode protection were SIBSas prepared in Example 8. Several tensile testing specimens were cutfrom the film and tested with a universal testing machine. The resultsindicate that this series of sulfonated elastomer films have an elasticdeformation from approximately 150% to 465%. The addition of up to 30%by weight of a conductive reinforcement material (CNTs, graphene, CNFs,etc.) and/or an inorganic additive typically reduces this elasticitydown to a reversible tensile strain from 6% to 110%. For electrochemicaltesting, the working electrodes (cathode layers) were prepared by mixing85 wt. % V₂O₅ or 88% of graphene-embraced V₂O₅ particles, 5-8 wt. %CNTs, and 7 wt. % polyvinylidene fluoride (PVDF) binder dissolved inN-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solidcontent. After coating the slurries on Al foil, the electrodes weredried at 120° C. in vacuum for 2 h to remove the solvent beforepressing. Then, the electrodes were cut into a disk (ϕ=12 mm) and driedat 100° C. for 24 h in vacuum.

Electrochemical measurements were carried out using CR2032 (3V)coin-type cells with lithium metal as the counter electrode (actually ananode of a Li-transition metal oxide cell), Celgard 2400 membrane asseparator, and 1 M LiPF₆ electrolyte solution dissolved in a mixture ofethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v).The cell assembly was performed in an argon-filled glove-box. The CVmeasurements were carried out using a CH-6 electrochemical workstationat a scanning rate of 1 mV/s. The electrochemical performance of thecell featuring sulfonated elastomer composite binder and that containingPVDF binder were evaluated by galvanostatic charge/discharge cycling ata current density of 50 mA/g using an Arbin electrochemical workstation.

Summarized in FIG. 3 are the specific intercalation capacity curves offour lithium cells: 2 cells each having a cathode containing V₂O₅particles (one cell having a sulfonated elastomer composite-basedlithium metal anode-protecting layer and the other not) and 2 cells eachhaving a cathode containing graphene-embraced V₂O₅ particles (one cellhaving a sulfonated elastomer composite-based lithium anode-protectinglayer and the other not). As the number of cycles increases, thespecific capacity of the un-protected cells drops at the fastest rate.In contrast, the presently invented sulfonated elastomer compositeprotection layer provides the battery cell with a significantly morestable and high specific capacity for a large number of cycles. Thesedata have clearly demonstrated the surprising and superior performanceof the presently invented sulfonated elastomer composite protectionapproach.

The sulfonated elastomer composite protective layer appears to becapable of reversibly deforming to a great extent without breakage whenthe lithium foil decreases in thickness during battery discharge. Theprotective layer also prevents the continued reaction between liquidelectrolyte and lithium metal at the anode, reducing the problem ofcontinuing loss in lithium and electrolyte. This also enables asignificantly more uniform deposition of lithium ions upon returningfrom the cathode during a battery re-charge step; hence, no lithiumdendrite. These were observed by using SEM to examine the surfaces ofthe electrodes recovered from the battery cells after some numbers ofcharge-discharge cycles.

Example 13: Sulfonated Elastomer Composite Implemented in the Anode of aLithium-LiCoO₂ Cell (Initially the Cell Anode has an Ultra-Thin LithiumLayer, <1 μm Thick)

The sulfonated elastomer composite as a lithium-protecting layer wasbased on the sulfonated polybutadiene (PB) prepared according to aprocedure used in Example 9. Tensile testing was also conducted on thesulfonated elastomer films (without the conductive reinforcementmaterial). This series of sulfonated elastomers can be elasticallystretched up to approximately 135% (having some lithium salt orconductive reinforcement material dispersed therein) or up to 770% (withno additive).

FIG. 4 shows that the cell having an anode-protecting polymer layeroffers a significantly more stable cycling behavior. The sulfonatedelastomer composite also acts to isolate the electrolyte from thelithium coating yet still allowing for easy diffusion of lithium ions.

Example 14: Li Metal Cells Containing Transition Metal FluorideNanoparticle-Based Cathode and a Sulfonated ElastomerComposite-Protected Lithium Metal Anode

This sulfonated elastomer composite layers were based on sulfonatedstyrene-butadiene-styrene triblock copolymer (SBS). Tensile testing wasconducted on some cut pieces of these layers. This series ofcross-linked polymers can be elastically stretched up to approximately820% (without any additive). The addition of additives results in anelasticity of approximately 5% (e.g. with 20% carbon black) to 160%(e.g. with 5% graphene sheets, as a conductive additive).

Commercially available powders of CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, andBiF₃ were subjected to high-intensity ball-milling to reduce theparticle size down to approximately 0.5-2.3 μm. Each type of these metalfluoride particles, along with graphene sheets (as a conductiveadditive), was then added into an NMP and PVDF binder suspension to forma multiple-component slurry. The slurry was then slurry-coated on Alfoil to form cathode layers.

Shown in FIG. 5 are the discharge capacity curves of two coin cellshaving the same cathode active material (FeF₃), but one cell having asulfonated elastomer composite-protected anode and the other having noprotective layer. These results have clearly demonstrated that thesulfonated elastomer composite protection strategy provides excellentprotection against capacity decay of a lithium metal battery.

The sulfonated elastomer composite appears to be capable of reversiblydeforming without breakage when the anode layer expands and shrinksduring charge and discharge. The polymer also prevents continuedreaction between the liquid electrolyte and the lithium metal. Nodendrite-like features were found with the anode being protected by asulfonated elastomer composite. This was confirmed by using SEM toexamine the surfaces of the electrodes recovered from the battery cellsafter some numbers of charge-discharge cycles.

Example 15: Li-Organic Cell Containing a Naphthalocyanine/ReducedGraphene Oxide (FePc/RGO) Particulate Cathode and a Protected Li FoilAnode

Particles of combined FePc/graphene sheets were obtained by ball-millinga mixture of FePc and RGO in a milling chamber for 30 minutes. Theresulting FePc/RGO mixture particles were potato-like in shape. Twolithium cells were prepared, each containing a Li foil anode, a porousseparator, and a cathode layer of FePc/RGO particles; one cellcontaining an anode-protecting layer and the other no protecting layer.

The cycling behaviors of these 2 lithium cells are shown in FIG. 6,which indicates that the lithium-organic cell having a sulfonatedelastomer composite protection layer in the anode exhibits asignificantly more stable cycling response. This protective layerreduces or eliminates the undesirable reactions between the lithiummetal and the electrolyte, yet the sulfonated elastomer layer itselfremains in ionic contact with the lithium metal and is permeable tolithium ions. This approach has significantly increased the cycle lifeof all lithium-organic batteries.

Example 16: Effect of Lithium Ion-Conducting Additive in a SulfonatedElastomer Composite

A wide variety of lithium ion-conducting additives were added to severaldifferent polymer matrix materials to prepare anode protection layers.The lithium ion conductivity vales of the resulting complex materialsare summarized in Table 1 below. We have discovered that these compositematerials are suitable anode-protecting layer materials provided thattheir lithium ion conductivity at room temperature is no less than 10⁻⁶S/cm. With these materials, lithium ions appear to be capable of readilydiffusing through the protective layer having a thickness no greaterthan 1 μm. For thicker polymer films (e.g. 10 μm), a lithium ionconductivity at room temperature of these sulfonated elastomercomposites no less than 10⁴ S/cm would be required.

TABLE 1 Lithium ion conductivity of various sulfonated elastomercomposite composite compositions as a lithium metal-protecting layer.Sample Lithium-conducting % sulfonated elastomer No. additive (1-2 μmthick) Li-ion conductivity (S/cm) E-1p Li₂CO₃ + (CH₂OCO₂Li)₂ 70-99% 1.3× 10⁻⁴ to 3.3 × 10⁻³ S/cm B1p LiF + LiOH + Li₂C₂O₄ 60-90% 4.2 × 10⁻⁵ to2.6 × 10⁻³ S/cm B2p LiF + HCOLi 80-99% 1.2 × 10⁻⁴ to 1.4 × 10⁻³ S/cm B3pLiOH 70-99% 8.5 × 10⁻⁴ to 1.1 × 10⁻² S/cm B4p Li₂CO₃ 70-99% 4.3 × 10⁻³to 9.5 × 10⁻³ S/cm B5p Li₂C₂O₄ 70-99% 8.2 × 10⁻⁴ to 1.3 × 10⁻² S/cm B6pLi₂CO₃ + LiOH 70-99% 1.5 × 10⁻³ to 1.7 × 10⁻² S/cm C1p LiClO₄ 70-99% 4.0× 10⁻⁴ to 2.2 × 10⁻³ S/cm C2p LiPF₆ 70-99% 2.1 × 10⁻⁴ to 6.2 × 10⁻³ S/cmC3p LiBF₄ 70-99% 1.2 × 10⁻⁴ to 1.7 × 10⁻³ S/cm C4p LiBOB + LiNO₃ 70-99%1.4 × 10⁻⁴ to 3.2 × 10⁻³ S/cm S1p Sulfonated polyaniline 85-99% 3.2 ×10⁻⁵ to 9.5 × 10⁻⁴ S/cm S2p Sulfonated PEEK 85-99% 1.4 × 10⁻⁴ to 1.3 ×10⁻³ S/cm S3p Sulfonated PVDF 80-99% 1.7 × 10⁻⁴ to 1.5 × 10⁻⁴ S/cm S4pPolyethylene oxide 80-99% 4.2 × 10⁻⁴ to 3.4 × 103⁴ S/cm

Example 17: Cycle Stability of Various Rechargeable Lithium BatteryCells

In lithium-ion battery industry, it is a common practice to define thecycle life of a battery as the number of charge-discharge cycles thatthe battery suffers a 20% decay in capacity based on the initialcapacity measured after the required electrochemical formation.Summarized in Table 2 below are the cycle life data of a broad array ofbatteries featuring an anode with or without an anode-protecting polymerlayer.

TABLE 2 Cycle life data of various lithium secondary (rechargeable)batteries. Initial Cycle life Anode-protecting Type & % of cathodeactive capacity (No. of Sample ID polymer material (mAh/g) cycles)CuCl₂-1e sulfonated elastomer 85% by wt. CuCl₂ particles (80 533 1455composite nm) + 7% graphite + 8% binder CuCl₂-2e none 85% by wt. CuCl₂particles (80 533 115 nm) + 7% graphite + 8% binder BiF₃- 1e none 85% bywt. BiFe₃ particles + 7% 275 115 graphene + 8% binder BiF₃-2e Sulfonatedelastomer 85% by wt. BiFe₃ particles + 7% 272 1,455 composite + 50%graphene + 8% binder ethylene oxide Li₂MnSiO₄- sulfonated elastomer 85%C-coated Li₂MnSiO₄ + 7% 250 2,475 1e composite CNT + 8% binderLi₂MnSiO₄- none 85% C-coated Li₂MnSiO₄ + 7% 252 543 2e CNT + 8% binderLi₆C₆O₆-1e sulfonated elastomer Li₆C₆O₆-graphene ball-milled 437 1,528composite + 20% polyaniline Li₆C₆O₆-2e none Li₆C₆O₆-graphene ball-milled438 116 MoS₂-1e sulfonated elastomer 85% MoS₂ + 8% graphite + 222 1,776composite binder MoS₂-2e none 85% MoS₂ + 8% graphite + 225 156 binder

In conclusion, the sulfonated elastomer composite-based anode-protectinglayer strategy is surprisingly effective in alleviating the problems oflithium metal dendrite formation and lithium metal-electrolyte reactionsthat otherwise lead to rapid capacity decay and potentially internalshorting and explosion of the lithium secondary batteries. Thesulfonated elastomer composite is capable of expanding or shrinkingcongruently or conformably with the anode layer. This capability helpsto maintain a good contact between the current collector (or the lithiumfilm itself) and the protective layer, enabling uniform re-deposition oflithium ions without interruption.

The anode-protecting layer appears to be capable of performing at leastthe following three functions:

-   -   1) Being highly elastic, the sulfonated elastomer composite        layer helps to maintain a good contact between a Li metal layer        (e.g. lithium metal foil, as the anode active material) and an        electrolyte phase (e.g. an electrolyte/separator assembly or a        solid-state electrolyte phase) when the Li metal layer decreases        in thickness (e.g. due to dissolution of Li in the electrolyte        when the battery is discharged) or increases in thickness (e.g.        due to re-deposition of lithium metal back to the Cu foil or the        lithium metal layer when the battery is recharged). The        sulfonated elastomer composite can expand and shrink responsive        to the shrinkage and expansion of the anode active material        layer. Such a conformal or congruent expansion/shrinkage of the        sulfonated elastomer composite helps to eliminate the potential        gap between the anode active material layer and the electrolyte        or separator, thereby maintaining the lithium ion migration        paths required of an operational Li metal battery.    -   2) The sulfonated elastomer matrix, infiltrated with a liquid        electrolyte (before, during, or after the cell is fabricated)        and coupled with its high-elasticity nature (good        electrode-electrolyte contact), enables the returning Li⁺ ions        to uniformly and successfully deposit back to the Li metal        surface or current collector surface, reducing the formation of        dead lithium particles, which otherwise become inactive. The        uniform deposition of Li metal also reduces the tendency to form        dangerous Li dendrites.    -   3) The presence of the conductive reinforcement material        (graphene sheets, CNTs, CNFs, etc.) are high-strength materials,        capable of stopping or deflecting the growth of dendrites (if        initiated), preventing the dendrite from penetrating the        separator to reach the cathode side to induce internal shorting,        which otherwise is a fire and explosion hazard.

We claim:
 1. A lithium metal secondary battery comprising a cathode, ananode, and a porous separator or electrolyte disposed between saidcathode and said anode, wherein said anode comprises: a) an anode activematerial layer containing a layer of lithium or lithium alloy, in a formof a foil, coating, or multiple particles aggregated together, as ananode active material; and b) an anode-protecting layer of a conductivesulfonated elastomer composite, disposed between said anode activematerial layer and said porous separator or electrolyte; wherein saidconductive sulfonated elastomer composite has from 0.01% to 40% byweight of a conductive reinforcement material and from 0.01% to 40% byweight of an electrochemically stable inorganic filler dispersed in asulfonated elastomeric matrix material, a thickness from 1 nm to 100 μm,a fully recoverable tensile strain from 2% to 500%, a lithium ionconductivity from 10⁻⁷ S/cm to 5×10⁻² S/cm, and an electricalconductivity from 10⁻⁷ S/cm to 100 S/cm when measured at roomtemperature, wherein said inorganic filler has a lithium intercalationpotential from 1.1 V to 4.5 V versus Li/Li⁺ and is selected from anoxide, carbide, boride, nitride, sulfide, phosphide, or selenide of atransition metal, a lithiated version thereof, or a combination thereof;wherein said lithium metal secondary battery does not include alithium-sulfur battery or lithium-selenium battery.
 2. The lithium metalsecondary battery of claim 1, wherein said transition metal is selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr,Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, combinations thereof, andcombinations thereof with Al, Ga, In, Sn, Pb, Sb, and Bi.
 3. The lithiummetal secondary battery of claim 1, wherein said inorganic filler isselected from nanodiscs, nanoplatelets, or nanosheets of (a) bismuthselenide or bismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,nickel, manganese, or any transition metal; (d) boron nitride, or (e) acombination thereof, wherein said nanodiscs, nanoplatelets, ornanosheets have a thickness from 1 nm to 100 nm.
 4. The lithium metalsecondary battery of claim 1, wherein said conductive reinforcementmaterial is selected from graphene sheets, carbon nanotubes, carbonnanofibers, carbon or graphite fibers, expanded graphite flakes, metalnanowires, conductive polymer fibers, or a combination thereof.
 5. Thelithium metal secondary battery of claim 1, wherein said sulfonatedelastomeric matrix material comprises a material selected from the groupconsisting of sulfonated version of natural polyisoprene, syntheticpolyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butylrubber, styrene-butadiene rubber, nitrile rubber, ethylene propylenerubber, ethylene propylene diene rubber, metallocene-basedpolyethylene-co-octene) elastomer, polyethylene-co-butene) elastomer,styrene-ethylene-butadiene-styrene elastomer, epichlorohydrin rubber,polyacrylic rubber, silicone rubber, fluorosilicone rubber,perfluoroelastomers, polyether block amides, chlorosulfonatedpolyethylene, ethylene-vinyl acetate, thermoplastic elastomer, proteinresilin, protein elastin, ethylene oxide-epichlorohydrin copolymer,polyurethane, urethane-urea copolymer, or a combination thereof.
 6. Thelithium metal secondary battery of claim 4, wherein said graphene sheetsare selected from the group consisting of pristine graphene, grapheneoxide, reduced graphene oxide, graphene fluoride, graphene chloride,nitrogenated graphene, hydrogenated graphene, doped graphene,functionalized graphene, and combinations thereof.
 7. The lithium metalsecondary battery of claim 4, wherein said graphene sheets comprisesingle-layer graphene or few-layer graphene, wherein said few-layergraphene is defined as a graphene platelet formed of less than 10graphene planes.
 8. The lithium metal secondary battery of claim 4,wherein said graphene sheets have a length or width from 5 nm to 5 μm.9. The lithium metal secondary battery of claim 1, wherein saidsulfonated elastomer composite further contains from 0.1% to 40% byweight of a lithium ion-conducting additive dispersed therein.
 10. Thelithium metal secondary battery of claim 1, wherein said sulfonatedelastomer composite contains a lithium ion-conducting additive dispersedtherein and is selected from the group consisting of Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, Li_(x)SO_(y), and combinations thereof, wherein X=F, Cl, I, or Br,R=a hydrocarbon group, 0<x≤1 and 1≤y≤4.
 11. The lithium metal secondarybattery of claim 1, wherein said conductive reinforcement material isselected from an electron-conducting polymer, a metal particle or wire,a graphene sheet, a carbon fiber, a graphite fiber, a carbon nanofiber,a graphite nanofiber, a carbon nanotube, a graphite particle, anexpanded graphite flake, an acetylene black particle, or a combinationthereof.
 12. The lithium metal secondary battery of claim 11, whereinsaid conductive reinforcement material has a thickness or diameter lessthan 100 nm.
 13. The lithium metal secondary battery of claim 1, whereinsaid sulfonated elastomer composite further contains a lithium saltdispersed therein and said lithium salt is selected from the groupconsisting of lithium perchlorate (LiClO₄), lithium hexafluorophosphate(LiPF₆), lithium borofluoride (LiBF₄), lithium hexafluoroarsenide(LiAsF₆), lithium trifluoro-methanesulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂), lithiumbis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF₂C₂O₄),lithium nitrate (LiNO₃), Li-fluoroalkyl-phosphate (LiPF₃(CF₂CF₃)₃),lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-basedlithium salt, or a combination thereof.
 14. The lithium metal secondarybattery of claim 1, wherein said sulfonated elastomer composite is mixedwith an electron-conducting polymer selected from polyaniline,polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonatedderivative thereof, or a combination thereof.
 15. The lithium metalsecondary battery of claim 1, wherein the sulfonated elastomer compositeforms a mixture or blend with a lithium ion-conducting polymer selectedfrom the group consisting of poly(ethylene oxide) (PEO), polypropyleneoxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate)(PMMA), poly(vinylidene fluoride) (PVDF), poly bis-methoxyethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane,poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonatedderivative thereof, and combinations thereof.
 16. The lithium metalsecondary battery of claim 1, wherein said anode-protecting layer has athickness from 1 nm to 10 μm.
 17. The lithium metal secondary battery ofclaim 1, wherein said cathode active material is selected from aninorganic material, an organic material, a polymeric material, or acombination thereof, and said inorganic material does not include sulfuror alkali metal polysulfide.
 18. The lithium metal secondary battery ofclaim 17, wherein said inorganic material is selected from the groupconsisting of metal oxide, metal phosphate, metal silicide, metalselenide, transition metal sulfide, and combinations thereof.
 19. Thelithium metal secondary battery of claim 17, wherein said inorganicmaterial is selected from the group consisting of lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,lithium metal silicide, and combinations thereof.
 20. The lithium metalsecondary battery of claim 17, wherein said inorganic material isselected from a metal fluoride or metal chloride including the groupconsisting of CoF₃, MnF₃, FeF₃, VF₃, VOF₃, TiF₃, BiF₃, NiF₂, FeF₂, CuF₂,CuF, SnF₂, AgF, CuCl₂, FeCl₃, MnCl₂, and combinations thereof.
 21. Thelithium metal secondary battery of claim 17, wherein said inorganicmaterial is selected from a lithium transition metal silicate, denotedas Li₂MSiO₄ or Li₂Ma_(x)Mb_(y)SiO₄, wherein M and Ma are selected fromFe, Mn, Co, Ni, V, or VO; Mb is selected from Fe, Mn, Co, Ni, V, Ti, Al,B, Sn, or Bi; and x+y≤1.
 22. The lithium metal secondary battery ofclaim 17, wherein said inorganic material is selected from the groupconsisting of transition metal dichalcogenide, a transition metaltrichalcogenide, and combinations thereof.
 23. The lithium metalsecondary battery of claim 17, wherein said inorganic material isselected from the group consisting of TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂,CoO₂, an iron oxide, a vanadium oxide, and combinations thereof.
 24. Thelithium metal secondary battery of claim 18, wherein said metal oxidecomprising a vanadium oxide selected from the group consisting of VO₂,Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉,Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃, their doped versions, their derivatives,and combinations thereof, wherein 0.1<x<5.
 25. The lithium metalsecondary battery of claim 18, wherein said metal oxide or metalphosphate is selected from the group consisting of layered compoundLiMO₂, spinel compound LiM₂O₄, olivine compound LiMPO₄, silicatecompound Li₂MSiO₄, tavorite compound LiMPO₄F, borate compound LiMBO₃,and combination thereofs, wherein M is a transition metal or a mixtureof multiple transition metals.
 26. The lithium metal secondary batteryof claim 17, wherein said inorganic material is selected from the groupconsisting of (a) bismuth selenide or bismuth telluride, (b) transitionmetal dichalcogenide or trichalcogenide, (c) sulfide, selenide, ortelluride of niobium, zirconium, molybdenum, hafnium, tantalum,tungsten, titanium, cobalt, manganese, iron, nickel, or a transitionmetal; (d) boron nitride, and (e) combinations thereof.
 27. The lithiummetal secondary battery of claim 17, wherein said organic material orpolymeric material is selected from the group consisting ofpoly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, and combinations thereof.
 28. The lithium metalsecondary battery of claim 27, wherein said thioether polymer isselected from the group consisting ofpoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).
 29. The lithium metalsecondary battery of claim 17, wherein said organic material comprises aphthalocyanine compound selected from the group consisting of copperphthalocyanine, zinc phthalocyanine, tin phthalocyanine, ironphthalocyanine, lead phthalocyanine, nickel phthalocyanine, vanadylphthalocyanine, fluorochromium phthalocyanine, magnesium phthalocyanine,manganous phthalocyanine, dilithium phthalocyanine, aluminumphthalocyanine chloride, cadmium phthalocyanine, chlorogalliumphthalocyanine, cobalt phthalocyanine, silver phthalocyanine, ametal-free phthalocyanine, a chemical derivative thereof, andcombinations thereof.
 30. The lithium metal secondary battery of claim1, wherein said cathode active material is in a form of nanoparticle,nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon,nanodisc, nanoplatelet, or nanohorn having a thickness or diameter from0.5 nm to 100 nm.
 31. The lithium metal secondary battery of claim 30,wherein said nanoparticle, nanowire, nanofiber, nanotube, nanosheet,nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn is coated withor embraced by a conductive protective coating selected from a carbonmaterial, graphene, electronically conductive polymer, conductive metaloxide, or conductive metal coating.